WidgyPageAdmin cant always check for review_queue

If widgy.contrib.review_queue is not in INSTALLED_APPS,
WidgyPageAdmin.has_review_queue() will throw a NameError whenever
an admin tries to edit a widgy page through the admin interface.

(cherry picked from commit b9c8ffa8aaf6c3ab58e3a4219d8b1f96035c3e1d)
Only set related_name on ProxyGenericRelation when absolutely necessary

To work around Django bugs in <1.6. Fixes #204 for Django >= 1.6.

(cherry picked from commit 18582c77f36d9af1ee93d79afa35941221ea32ab)

This merges #264 and fixes #204.

Reviewed-By: Antoine Catton <acatton@fusionbox.com>
(cherry picked from commit 8b0e6ac646d3dace26b3b868701163d20aa0634e)
Only import from review_queue when it is installed

(cherry picked from commit 8cd14ea852e24a22dfdd96f3d4061b45c57273cf)
Changlog for 0.3.2

(cherry picked from commit cd350ad75b5719908e628835bd0b4a17b4894dc7)
Version 0.3.2