Django 1.9 replaced Field.rel with Field.remote_field, along with a

handful of other attributes, as part of an effort to provide a

supported, documented API for field relations.
This change adds compatibility with both the old undocumented API and

the new documented API through the addition of get_remote_field() and

get_remote_field_model() functions. These are used instead of

.rel/.rel.to and .remote_field/.remote_field.model accessors.

Unit tests pass on Django 1.6 through 1.11, and 2.1 with additional

changes.