The old names were downright confusing. Some seemed to mean the opposite
of what the class actually did.
The new names follow a consistent nomenclature:
(Forward|Reverse)(ManyToOne|OneToOne|ManyToMany)Descriptor.
I mentioned combinations that do not exist in the docstring in order to
help people who would search for them in the code base.
At 2800 lines it was the largest module in the django package. This
commit brings it down to a more manageable 1620 lines.
Very small changes were performed to uniformize import style.
Tim Graham
Simon Charette
Aymeric Augustin