Fixed issue where SortableGenericInlines would break whenever adding blank inline forms.

This is because inline fieldset names append the names of the generic relation fields as defined in models.py. For instance, instead of being called "model_set-n-field" they'd be called
"app-model-content_type-object_id-n-field" reflecting the names of the generic type and id fields. I replaced the string split on '-' with a regexp split that looks for the -n- pattern instead.

This appears to work in Chrome for both regular and generic relations.
Better handling of checkboxes in sortable inline forms.

Previously sortable.js was unable to detect whether or not a checkbox had deviated from its original value. First of all the test to find non-blank values:

$set_block.find(":input[value!=''][type!='hidden']")

would not work on a checkbox, since its value will evaluate to "on" or "off".
Secondly, the function filter_unchanged only handled select boxes and the sortable field. As a result, a checkbox in an inline form would always flag a row as "changed". This is particularily troublesome when you have extra blank forms in a formset.

The fix was to add a block in filter_unchanged to check for a checkbox field, and compare its current checked property to that of defaultChecked.
Merge branch 'develop' of https://github.com/sixthgear/django-suit into sixthgear-develop
Merge branch 'sixthgear-develop' into develop