Added a quick test to check the managers behaviour with unique nullable fields. This passes locally with sqlite, let's see what travis has to say about mysql.
Only fallback when there is no value for a given translation or the value is the field's default.
For CharField(null=True) the default is None, so empty string becomes a proper value (it's sometimes useful to treat it differently than None).
Test for the nullable CharField case.
Added a fallback_undefined option to allow customizing the value that triggers falling back.
Flake8, overindented continuation line.
Implemented a widget that shows a clear checkbox for any non-required form field.
Overriden admin widgets of CharFields and TextFields and patched forms.CharField for nullable fields, so undefined translations don't get filled with empty strings when an admin form is saved (thus becoming defined in the case of a nullable field).
Replaced format_html with mark_safe/conditional_escape for Django < 1.5 compatibility.
Made the widget template for nullable fields unicode, so the widget renders with non-ascii characters in input value.
Use proper assert* methods in test.

This remove PendingDeprecationWarnings.
Added convenience admin classes for easier inclusion of tabbed translation fields static files (closes #171).
Added docs for tabbed translation fields admin classes.
Fixed wrong use of inline literal.
Fixed typo and made a small reword.
Fix _mt_init attribute deletion (close #176).
Initial work towards python 3 support
Fixed flake8 complaints.
Use six.with_metaclass instead of some hack.
Further work towards Python 3 support.
Preserve default fields order in group_fieldsets.
Update tox.ini.