Fixed #3439: vastly improved the performance of django.dispatch (and added tests!). Thanks to Brian Harring for the patch.  Note that one of the new tests fails under sqlite currently; it's not clear if this is a sqlite problem or a problem with the tests, but it appears not to be a problem with the dispatcher itself.


git-svn-id: http://code.djangoproject.com/svn/django/trunk@4588 bcc190cf-cafb-0310-a4f2-bffc1f526a37