[1.2.X] Fixed #14303 -- Ensure that the ids created for new inlines are unique...

[1.2.X] Fixed #14303 -- Ensure that the ids created for new inlines are unique after interstitial deletions have occurred. Thanks to m0nonoke for the report, and Julien Phalip for the patch.

Backport of r15422 from trunk.

git-svn-id: http://code.djangoproject.com/svn/django/branches/releases/1.2.X@15423 bcc190cf-cafb-0310-a4f2-bffc1f526a37