Merge pull request #2218 from yakky/feature/test_2215

Test for #2215
Add django-trunk to build matrix
Fix django 1.6 incompatible `exclude` attribute in `stacks` forms
Fix django 1.6-incompatible changelist queryset attribute naming
Added django 1.6 compat fix for ModelAdmin metaclass
Fix django 1.6 urls imports
Fix BooleanField default value as per django 1.6 changes
Use django 1.6 compatible json
Take into account the new django branch model
Update django-reversion version in requirements
Restore Django 1.4 compatibility
Allow failures on django 1.6 tests
Always use Page as revision-ed object
Added requirements for selenium+django 1.6
Django 1.6 compatible requirements
Import fixes
Fix new Model.save_base() signature
Move Django version checking to cms.utils.compat module
Temporary switch test requirements