Change direct message count limiting to work the same as the real twitter api for FakeTwitterAPI
Add _dm_or_404 helper to FakeTwitterAPI for consistency
Explanatory comments in FakeTwitterAPI for twitter's response wierdness for forbidden DM access
Merge branch 'feature/issue-9-add-direct-message-support-to-the-fake-twitter-api' into feature/issue-11-tests-for-uncovered-things-in-fake-twitter

Conflicts:
	txtwitter/tests/test_fake_twitter.py