Fixed warnings: 1_6.W001 and RemovedInDjango18Warning
Added python 3 support for travis-ci (and let them fail for now).

test_test (test_project.test_app.tests.TestTestApp) ... /Volumes/Shared HD/Developing/py/django-interval-field/test_project/test_app/views.py:8: RemovedInDjango18Warning: Creating a ModelForm without either the 'fields' attribute or the 'exclude' attribute is deprecated - form TestForm needs updating

?: (1_6.W001) Some project unittests may not execute as expected.
	HINT: Django 1.6 introduced a new default test runner. It looks like this project was generated using Django 1.5 or earlier. You should ensure your tests are all running & behaving as expected. See https://docs.djangoproject.com/en/dev/releases/1.6/#new-test-runner for more information.