Fixed #14427 -- Added --bisect and --pair flags to runtests.py, making it...

Fixed #14427 -- Added --bisect and --pair flags to runtests.py, making it easier to find pairs of tests that fail when run together.

git-svn-id: http://code.djangoproject.com/svn/django/trunk@14079 bcc190cf-cafb-0310-a4f2-bffc1f526a37