[1.6.x] Fixed #18285 -- Documented that bulk_create doesn't work with M2M relationships.

Backport of 9173d2cb74 from master
[1.6.x] Fixed #20052 -- Discouraged use of Jython given the current state of django-jython.

Thanks Josh Juneau (maintainer of django-jython) for the review.

Backport of a67e327db5 from master
[1.6.x] Fixed #13116 -- Described scope of variables created by {% url ... as var %} syntax.

Thanks leif_p for the suggestion.

Backport of 4a5aac47a6 from master
[1.6.x] Fixed #18942 -- Clarified usage of {% get_static_prefix %}.

Thanks Aymeric for the suggestion.

Backport of bc7668eb51 from master