Fix missing bits of test

Travis will now grab the newest point releases of Django, including 1.6.5

Also added 'bootstrapform' to test settings to reduce failing tests to actual bugs
Remove --use-mirrors
Grab requirements.txt for tests and remove Django 1.3 testing (requirements.txt asks for Django>1.4)
Give CustomField.empty_selection_list a default value

BooleanField defaults to False <1.6 and to None >=1.6, causing tests to fail on 1.6
Merge pull request #214 from Inboxen/testing-fixes

Testing fixes