updated for version 7.3.500
Problem:    Ming makefile unconditionally sets WINVER.
Solution:   Only defined when not already defined. (Yasuhiro Matsumoto)
diff --git a/src/version.c b/src/version.c
index df3717a..720e45a 100644
--- a/src/version.c
+++ b/src/version.c
@@ -715,6 +715,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    500,
+/**/
     499,
 /**/
     498,