Fix some minor Tramp problems

* lisp/net/tramp-gvfs.el (tramp-gvfs-maybe-open-connection):
Check, that `tramp-password-save-function' is a function.

* lisp/net/tramp-smb.el (tramp-smb-handle-file-system-info):
Check, that there is a share.

* lisp/net/tramp.el (outline-regexp): Declare.
(tramp-get-debug-buffer): Let-bind `signal-hook-function'.

* test/lisp/net/tramp-tests.el (tramp-test04-substitute-in-file-name):
Skip some tests for Emacs 24 and 25; they let Emacs crash.

lisp/net/tramp-gvfs.el

@@ -1911,7 +1911,9 @@ connection if a previous connection has died for some reason."
 	  (tramp-error vec 'file-error "FUSE mount denied"))
 
 	;; Save the password.
-	(ignore-errors (funcall tramp-password-save-function))
+	(ignore-errors
+	  (and (functionp tramp-password-save-function)
+	       (funcall tramp-password-save-function)))
 
 	;; Set connection-local variables.
 	(tramp-set-connection-local-variables vec)

lisp/net/tramp-smb.el

@@ -946,29 +946,31 @@ PRESERVE-UID-GID and PRESERVE-EXTENDED-ATTRIBUTES are completely ignored."
     (unless (file-directory-p filename)
       (setq filename (file-name-directory filename)))
     (with-parsed-tramp-file-name (expand-file-name filename) nil
-      (tramp-message v 5 "file system info: %s" localname)
-      (tramp-smb-send-command v (format "du %s/*" (tramp-smb-get-localname v)))
-      (with-current-buffer (tramp-get-connection-buffer v)
-	(let (total avail blocksize)
-	  (goto-char (point-min))
-	  (forward-line)
-	  (when (looking-at
-		 (eval-when-compile
-		   (concat "[[:space:]]*\\([[:digit:]]+\\)"
-			   " blocks of size \\([[:digit:]]+\\)"
-			   "\\. \\([[:digit:]]+\\) blocks available")))
-	    (setq blocksize (string-to-number (match-string 2))
-		  total (* blocksize (string-to-number (match-string 1)))
-		  avail (* blocksize (string-to-number (match-string 3)))))
-	  (forward-line)
-	  (when (looking-at "Total number of bytes: \\([[:digit:]]+\\)")
-	    ;; The used number of bytes is not part of the result.  As
-	    ;; side effect, we store it as file property.
-	    (tramp-set-file-property
-	     v localname "used-bytes" (string-to-number (match-string 1))))
-	  ;; Result.
-	  (when (and total avail)
-	    (list total (- total avail) avail)))))))
+      (when (tramp-smb-get-share v)
+	(tramp-message v 5 "file system info: %s" localname)
+	(tramp-smb-send-command
+	 v (format "du %s/*" (tramp-smb-get-localname v)))
+	(with-current-buffer (tramp-get-connection-buffer v)
+	  (let (total avail blocksize)
+	    (goto-char (point-min))
+	    (forward-line)
+	    (when (looking-at
+		   (eval-when-compile
+		     (concat "[[:space:]]*\\([[:digit:]]+\\)"
+			     " blocks of size \\([[:digit:]]+\\)"
+			     "\\. \\([[:digit:]]+\\) blocks available")))
+	      (setq blocksize (string-to-number (match-string 2))
+		    total (* blocksize (string-to-number (match-string 1)))
+		    avail (* blocksize (string-to-number (match-string 3)))))
+	    (forward-line)
+	    (when (looking-at "Total number of bytes: \\([[:digit:]]+\\)")
+	      ;; The used number of bytes is not part of the result.
+	      ;; As side effect, we store it as file property.
+	      (tramp-set-file-property
+	       v localname "used-bytes" (string-to-number (match-string 1))))
+	    ;; Result.
+	    (when (and total avail)
+	      (list total (- total avail) avail))))))))
 
 (defun tramp-smb-handle-file-writable-p (filename)
   "Like `file-writable-p' for Tramp files."

lisp/net/tramp.el

@@ -64,6 +64,7 @@
 (require 'cl-lib)
 (declare-function netrc-parse "netrc")
 (defvar auto-save-file-name-transforms)
+(defvar outline-regexp)
 
 ;;; User Customizable Internal Variables:
 
@@ -1650,7 +1651,8 @@ The outline level is equal to the verbosity of the Tramp message."
       ;; Furthermore, `outline-regexp' must have the correct value
       ;; already, because it is used by `font-lock-compile-keywords'.
       (let ((default-directory (tramp-compat-temporary-file-directory))
-	    (outline-regexp tramp-debug-outline-regexp))
+	    (outline-regexp tramp-debug-outline-regexp)
+	    signal-hook-function)
 	(outline-mode))
       (set (make-local-variable 'outline-regexp) tramp-debug-outline-regexp)
       (set (make-local-variable 'outline-level) 'tramp-debug-outline-level)

test/lisp/net/tramp-tests.el

@@ -1956,36 +1956,40 @@ properly.  BODY shall not contain a timeout."
       (substitute-in-file-name "/method:host:/:/path//foo")
       "/method:host:/:/path//foo"))
 
-    (should
-     (string-equal (substitute-in-file-name "/method:host://~foo") "/~foo"))
-    (should
-     (string-equal
-      (substitute-in-file-name "/method:host:/~foo") "/method:host:/~foo"))
-    (should
-     (string-equal
-      (substitute-in-file-name "/method:host:/path//~foo") "/~foo"))
-    ;; (substitute-in-file-name "/path/~foo") expands only for a local
-    ;; user "foo" to "/~foo"".  Otherwise, it doesn't expand.
-    (should
-     (string-equal
-      (substitute-in-file-name
-       "/method:host:/path/~foo") "/method:host:/path/~foo"))
-    ;; Quoting local part.
-    (should
-     (string-equal
-      (substitute-in-file-name "/method:host:/://~foo")
-      "/method:host:/://~foo"))
-    (should
-     (string-equal
-      (substitute-in-file-name "/method:host:/:/~foo") "/method:host:/:/~foo"))
-    (should
-     (string-equal
-      (substitute-in-file-name
-       "/method:host:/:/path//~foo") "/method:host:/:/path//~foo"))
-    (should
-     (string-equal
-      (substitute-in-file-name
-       "/method:host:/:/path/~foo") "/method:host:/:/path/~foo"))
+    ;; Forwhatever reasons, the following tests let Emacs crash for
+    ;; Emacs 24 and Emacs 25, occasionally. No idea what's up.
+    (when (or (tramp--test-emacs26-p) (tramp--test-emacs27-p))
+      (should
+       (string-equal (substitute-in-file-name "/method:host://~foo") "/~foo"))
+      (should
+       (string-equal
+	(substitute-in-file-name "/method:host:/~foo") "/method:host:/~foo"))
+      (should
+       (string-equal
+	(substitute-in-file-name "/method:host:/path//~foo") "/~foo"))
+      ;; (substitute-in-file-name "/path/~foo") expands only for a local
+      ;; user "foo" to "/~foo"".  Otherwise, it doesn't expand.
+      (should
+       (string-equal
+	(substitute-in-file-name
+	 "/method:host:/path/~foo") "/method:host:/path/~foo"))
+      ;; Quoting local part.
+      (should
+       (string-equal
+	(substitute-in-file-name "/method:host:/://~foo")
+	"/method:host:/://~foo"))
+      (should
+       (string-equal
+	(substitute-in-file-name
+	 "/method:host:/:/~foo") "/method:host:/:/~foo"))
+      (should
+       (string-equal
+	(substitute-in-file-name
+	 "/method:host:/:/path//~foo") "/method:host:/:/path//~foo"))
+      (should
+       (string-equal
+	(substitute-in-file-name
+	 "/method:host:/:/path/~foo") "/method:host:/:/path/~foo")))
 
     (let (process-environment)
       (should