[1.2.X] Fixed #14427 -- Added --bisect and --pair flags to runtests.py, making...

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

Backport of r14079 from trunk.

git-svn-id: http://code.djangoproject.com/svn/django/branches/releases/1.2.X@14081 bcc190cf-cafb-0310-a4f2-bffc1f526a37