updated for version 7.3.507
Problem:    When exiting with unsaved changes, selecting an existing file in
            the file dialog, there is no dialog to ask whether the existing
            file should be overwritten. (Felipe G. Nievinski)
Solution:   Call check_overwrite() before writing. (Christian Brabandt)
diff --git a/src/proto/ex_cmds.pro b/src/proto/ex_cmds.pro
index ff868ca..1669d79 100644
--- a/src/proto/ex_cmds.pro
+++ b/src/proto/ex_cmds.pro
@@ -23,6 +23,7 @@
 void ex_update __ARGS((exarg_T *eap));
 void ex_write __ARGS((exarg_T *eap));
 int do_write __ARGS((exarg_T *eap));
+int check_overwrite __ARGS((exarg_T *eap, buf_T *buf, char_u *fname, char_u *ffname, int other));
 void ex_wnext __ARGS((exarg_T *eap));
 void do_wqall __ARGS((exarg_T *eap));
 int not_writing __ARGS((void));