Add unit tests for edit_handlers.py. Lint edit_handlers.py.
Merge branch 'master' into edit-handlers-unit-tests

Conflicts:
	wagtail/wagtailadmin/edit_handlers.py
Remove broken test
Update edit handlers unit tests

Add more tests. Clean up modified class properties after tests finish.
Replace assertRegexpMatches with assertIn.
Merge branch 'master' into edit-handlers-unit-tests
Fix Travis test failures
Reorganise unit tests to obviate the use of del
Merge pull request #335 from mope/edit-handlers-unit-tests

Add unit tests for edit_handlers.py. Lint edit_handlers.py.