eshell: Add 'rgrep' builtin

* lisp/eshell/em-unix.el (eshell/rgrep): New function.
(eshell-unix-initialize): Add "rgrep" to 'eshell-complex-commands'.

* etc/NEWS: Add NEWS entry for rgrep.

* doc/misc/eshell.texi (Built-ins): Add documentation for rgrep.

doc/misc/eshell.texi

@@ -602,6 +602,8 @@ disabled by default.
 @cmindex egrep
 @itemx fgrep
 @cmindex fgrep
+@itemx rgrep
+@cmindex rgrep
 @itemx glimpse
 @cmindex glimpse
 The @command{grep} commands are compatible with GNU @command{grep},

etc/NEWS

@@ -174,6 +174,11 @@ correctly unloads Eshell and all of its modules.
 After manually editing 'eshell-aliases-file', you can use this command
 to load the edited aliases.
 
++++
+*** 'rgrep' is now a builtin command.
+Running "rgrep" in Eshell now uses the Emacs grep facility instead of
+calling external rgrep.
+
 ** Shell Mode
 
 +++

lisp/eshell/em-unix.el

@@ -145,9 +145,10 @@ Otherwise, Emacs will attempt to use rsh to invoke du on the remote machine."
     (add-hook 'pcomplete-try-first-hook
 	      'eshell-complete-host-reference nil t))
   (setq-local eshell-complex-commands
-	(append '("grep" "egrep" "fgrep" "agrep" "glimpse" "locate"
-		  "cat" "time" "cp" "mv" "make" "du" "diff")
-		eshell-complex-commands)))
+	      (append '("grep" "egrep" "fgrep" "agrep" "rgrep"
+                        "glimpse" "locate" "cat" "time" "cp" "mv"
+                        "make" "du" "diff")
+		      eshell-complex-commands)))
 
 (defalias 'eshell/date     'current-time-string)
 (defalias 'eshell/basename 'file-name-nondirectory)
@@ -773,6 +774,10 @@ external command."
   "Use Emacs grep facility instead of calling external agrep."
   (eshell-grep "agrep" args))
 
+(defun eshell/rgrep (&rest args)
+  "Use Emacs grep facility instead of calling external rgrep."
+  (eshell-grep "grep" (append '("-rH") args) t))
+
 (defun eshell/glimpse (&rest args)
   "Use Emacs grep facility instead of calling external glimpse."
   (let (null-device)