flatatt - Switch to from django.form.utils to internal app .utils
Avoid side effects when manipulating context in layout objects

Added a `KeepContext` context manager, that rolls back changes done to
context by layout objects, to avoid side effects in other layout
objects.

This allows the cleanup of some code and simplifies writing safe layout
objects, like the one proposed in issue #136.
Fixing Python 2.5 compatibility
Merge branch 'dev' of git://github.com/rockingskier/django-crispy-forms into dev
Updated CHANGELOG and CONTRIBUTORS