Update check_for_receivers for django 1.6.
Fix AttributeError in django 1.6.

rel_name is not available on BaseInlineFormSet as of
https://github.com/django/django/commit/3647c0a49a2f4535b8a9aba40e662743e4d53e76
Add TravisCI config.
Merge pull request #252 from meshy/django-1.6

Django 1.6