Added missing method in the dummy database backend.
Fixed #19997 -- Added custom EMPTY_VALUES to form fields

Thanks Loic Bistuer for the report and the patch.
Fix 19916. Smarter tokenizing of contrib.comment's templatetags arguments.
Added a ManyToManyField(db_constraint=False) option, this allows not creating constraints on the intermediary models.
Adde two "versionadded" markers, thanks to mYk for noticing.
Merge pull request #850 from bmispelon/ticket-19916

Fix 19916. Smarter tokenizing of contrib.comment's templatetags arguments
Fixed #15363 -- Renamed and normalized to `get_queryset` the methods that return a QuerySet.
Fixed a regression in forms changed_data

Thanks Loic Bistuer for spotting the regression and the initial
patch. Refs #16612.
Replaced proj4 testing by a regex