Fix myisam_crash_before_flush_keys on Windows

Problem : mtr reports test failure because it sees
[ERROR] mysqld got exception 0x80000003 ;
in the .err file

The exception comes from DBUG_EXECUTE_IF (.. abort())

Fix:  use DBUG_ABORT instead of abort() - it does not throw 
any exceptions.

storage/myisam/mi_close.c

@@ -61,7 +61,7 @@ int mi_close(register MI_INFO *info)
   if (flag)
   {
     DBUG_EXECUTE_IF("crash_before_flush_keys",
-                    if (share->kfile >= 0) abort(););
+                    if (share->kfile >= 0) DBUG_ABORT(););
     if (share->kfile >= 0 &&
 	flush_key_blocks(share->key_cache, share->kfile,
                          ((share->temporary || share->deleting) ?