files: alert the user afterward when an overwritten file is being edited

(The ideal behavior would be that nano would warn the user beforehand,
before the file that is being edited by someone else gets overwritten,
but that would require many more changes.  So... just give a helpful
warning -- that's already better than it was.)

src/files.c

@@ -291,7 +291,7 @@ int delete_lockfile(const char *lockfilename)
 /* Deal with lockfiles.  Return -1 on refusing to override the lockfile,
  * and 1 on successfully creating it; 0 means we were not successful in
  * creating the lockfile but we should continue to load the file. */
-int do_lockfile(const char *filename)
+int do_lockfile(const char *filename, bool ask_the_user)
 {
 	char *namecopy = copy_of(filename);
 	char *secondcopy = copy_of(filename);
@@ -305,7 +305,9 @@ int do_lockfile(const char *filename)
 	snprintf(lockfilename, locknamesize, "%s/%s%s%s", dirname(namecopy),
 				locking_prefix, basename(secondcopy), locking_suffix);
 
-	if (stat(lockfilename, &fileinfo) != -1) {
+	if (!ask_the_user && stat(lockfilename, &fileinfo) != -1) {
+		warn_and_shortly_pause(_("Someone else is also editing this file"));
+	} else if (stat(lockfilename, &fileinfo) != -1) {
 		size_t readtot = 0;
 		size_t readamt = 0;
 		char *lockbuf, *question, *pidstring, *postedname, *promptstr;
@@ -457,7 +459,7 @@ bool open_buffer(const char *filename, bool new_buffer)
 #ifndef NANO_TINY
 			if (ISSET(LOCKING) && filename[0] != '\0') {
 				/* When not overriding an existing lock, discard the buffer. */
-				if (do_lockfile(realname) < 0) {
+				if (do_lockfile(realname, TRUE) < 0) {
 #ifdef ENABLE_MULTIBUFFER
 					if (openfile != openfile->next)
 						close_buffer();
@@ -1875,7 +1877,7 @@ bool write_file(const char *name, FILE *thefile, bool tmp,
 				delete_lockfile(openfile->lock_filename);
 				free(openfile->lock_filename);
 				openfile->lock_filename = NULL;
-				do_lockfile(realname);
+				do_lockfile(realname, FALSE);
 			}
 #endif
 #ifdef ENABLE_COLOR