Add the option to not create lockfiles

* src/filelock.c (syms_of_filelock): New boolean create-lockfiles.
(lock_file): If create_lockfiles is 0, do nothing.

* lisp/cus-start.el (create-lockfiles): Add it.

Fixes: debbugs:11227

lisp/ChangeLog

@@ -1,3 +1,7 @@
+2012-05-10  Dave Abrahams  <dave@boostpro.com>
+
+	* cus-start.el (create-lockfiles): Add it.
+
 2012-05-09  Chong Yidong  <cyd@gnu.org>
 
 	* net/browse-url.el (browse-url-url-encode-chars): Use upper-case.

lisp/cus-start.el

@@ -204,6 +204,7 @@ Leaving \"Default\" unchecked is equivalent with specifying a default of
 	     (delete-by-moving-to-trash auto-save boolean "23.1")
 	     (auto-save-visited-file-name auto-save boolean)
 	     ;; filelock.c
+	     (create-lockfiles files boolean "24.2")
 	     (temporary-file-directory
 	      ;; Darwin section added 24.1, does not seem worth :version bump.
 	      files directory nil

src/ChangeLog

@@ -1,3 +1,8 @@
+2012-05-10  Dave Abrahams  <dave@boostpro.com>
+
+	* filelock.c (syms_of_filelock): New boolean create-lockfiles.
+	(lock_file): If create_lockfiles is 0, do nothing.  (Bug#11227)
+
 2012-05-09  Michael Albinus  <michael.albinus@gmx.de>
 
 	* dbusbind.c (xd_registered_buses): New internal Lisp object.

src/filelock.c

@@ -550,6 +550,10 @@ lock_file (Lisp_Object fn)
   struct gcpro gcpro1;
   USE_SAFE_ALLOCA;
 
+  /* Don't do locking if the user has opted out.  */
+  if (! create_lockfiles)
+    return;
+
   /* Don't do locking while dumping Emacs.
      Uncompressing wtmp files uses call-process, which does not work
      in an uninitialized Emacs.  */
@@ -722,6 +726,10 @@ syms_of_filelock (void)
 	       doc: /* The directory for writing temporary files.  */);
   Vtemporary_file_directory = Qnil;
 
+  DEFVAR_BOOL ("create-lockfiles", create_lockfiles,
+	       doc: /* Non-nil means use lockfiles to avoid editing collisions.  */);
+  create_lockfiles = 1;
+
 #ifdef CLASH_DETECTION
   defsubr (&Sunlock_buffer);
   defsubr (&Slock_buffer);