Added the ability to specify multiple ports available for the...

Added the ability to specify multiple ports available for the `LiveServerTestCase` WSGI server. This allows multiple processes to run the tests simultaneously and is particularly useful in a continuous integration context. Many thanks to Aymeric Augustin for the suggestions and feedback.

git-svn-id: http://code.djangoproject.com/svn/django/trunk@17289 bcc190cf-cafb-0310-a4f2-bffc1f526a37