Docstring instead of comment for helpers._Default.
Tests and docs for MessageDispatchHelper.
Tiny docstring cleanups.
Remove some dead code.
Merge branch 'feature/issue-707-test-helper-tests-and-docs-1' into develop
twitter transport test fixes after txTwitter 0.1.1a release (thanks @jerith)
Merge branch 'develop' of github.com:praekelt/vumi into develop
Merge branch 'develop' into feature/issue-711-strip-at-to-addr-from-content-when-publishing-message-for-twitter-transport

Conflicts:
	vumi/transports/twitter/tests/test_twitter.py