updated for version 7.4.684
Problem:    When starting several Vim instances in diff mode, the temp files
            used may not be unique. (Issue 353)
Solution:   Add an argument to vim_tempname() to keep the file.
diff --git a/src/os_unix.c b/src/os_unix.c
index df045a5..57c013f 100644
--- a/src/os_unix.c
+++ b/src/os_unix.c
@@ -5838,7 +5838,7 @@
     /*
      * get a name for the temp file
      */
-    if ((tempname = vim_tempname('o')) == NULL)
+    if ((tempname = vim_tempname('o', FALSE)) == NULL)
     {
 	EMSG(_(e_notmp));
 	return FAIL;