[1.2.X] Fixed #14025 -- Modified flush to adhere to router sync instructions...

[1.2.X] Fixed #14025 -- Modified flush to adhere to router sync instructions when emmiting post-sync signals. Thanks to linovia for the patch.

Backport of r13466 from trunk.

git-svn-id: http://code.djangoproject.com/svn/django/branches/releases/1.2.X@13467 bcc190cf-cafb-0310-a4f2-bffc1f526a37