Fixes #139 Search form doesn't submit filters on IE10
Fixes #140 KeyError when using MPTTModelAdmin and SortableModelAdmin
together. Bug appeared due to changes in latest MPTT library.
Looks like get_changelist_form() form variable override is no longer
needed and removing it fixes the KeyError problem.
JS: Sortable JS improvement that fixes empty inline creation when
saving inlines with blank inputs.
Version bump to 0.2.4 and changelog updates
Merge branch 'develop'