Add Django 1.9 compatibility

[encolpe]

Little fix to use multiforms with Django 1.9

[encolpe]

I don't like the fuzzy pattern try/except as we know that the renaming was done for the 1.9 version. IMHO it's an important information for the maintainance that we can remove the condition if we not support Django 1.8 in the future.

[bmispelon]

I agree with @MarkusH here. It's better to test for the feature than the version in my experience.

A comment about version support would help cleaning up the conditional imports when we support supporting older Django versions (that could also be achieved by looking at git blame).

[encolpe]

Explicit is better than implicit. We can give the information directly, let's do it. The try/except mechanism is done to handle unexpected comportment in a way we can handle not to write less code for expected comportment.

After that, you can split hairs in four as you wish.