Doc tweaks related to file locking

* doc/lispref/files.texi (File Locks): All systems support locking.

* src/filelock.c (Flock_buffer): Doc tweak.

doc/lispref/ChangeLog

@@ -1,3 +1,7 @@
+2014-03-26  Glenn Morris  <rgm@gnu.org>
+
+	* files.texi (File Locks): All systems support locking.
+
 2014-03-22  Glenn Morris  <rgm@gnu.org>
 
 	* commands.texi (Defining Commands):

doc/lispref/files.texi

@@ -709,15 +709,15 @@ some other job.
 This function locks the file @var{filename}, if the current buffer is
 modified.  The argument @var{filename} defaults to the current buffer's
 visited file.  Nothing is done if the current buffer is not visiting a
-file, or is not modified, or if the system does not support locking.
+file, or is not modified, or if the option @code{create-lockfiles} is
+@code{nil}.
 @end defun
 
 @defun unlock-buffer
 This function unlocks the file being visited in the current buffer,
 if the buffer is modified.  If the buffer is not modified, then
 the file should not be locked, so this function does nothing.  It also
-does nothing if the current buffer is not visiting a file, or if the
-system does not support locking.
+does nothing if the current buffer is not visiting a file, or is not locked.
 @end defun
 
 @defopt create-lockfiles

src/ChangeLog

@@ -1,5 +1,7 @@
 2014-03-26  Glenn Morris  <rgm@gnu.org>
 
+	* filelock.c (Flock_buffer): Doc tweak.
+
 	* buffer.c (Frestore_buffer_modified_p, Fkill_buffer):
 	* emacs.c (shut_down_emacs):
 	* fileio.c (Finsert_file_contents, write_region):

src/filelock.c

@@ -771,7 +771,9 @@ DEFUN ("lock-buffer", Flock_buffer, Slock_buffer,
        0, 1, 0,
        doc: /* Lock FILE, if current buffer is modified.
 FILE defaults to current buffer's visited file,
-or else nothing is done if current buffer isn't visiting a file.  */)
+or else nothing is done if current buffer isn't visiting a file.
+
+If the option `create-lockfiles' is nil, this does nothing.  */)
   (Lisp_Object file)
 {
   if (NILP (file))