Define the SessionStore inside __init__ instead of process_request

It's unnecessary to run this on every request, since technically, settings *should be* immutable.
Stopped calling loaddata with commit=False.

This was a stealth option only used by the tests, and it isn't useful
any more since `atomic` provides nested transactions.
Introduced getters for connection.autocommit and .needs_rollback.

They ensure that the attributes aren't accessed in conditions where they
don't contain a valid value.

Fixed #20666.
Removed a comment that wasn't adding a value.

In the intervening years, RelatedField has become less of a hack (though it still is one). Anyone who wants to can re-instate the comment, but please add more details.
Updated FAQ on Python versions to explain 2 vs 3.

Required the latest version for each Python series to minimize
bookkeeping in the future.

Forward-port of c1d8f3b from stable/1.6.x.
Stopped branding Python 3 support as experimental.

Forward-port of 0de21a6 from stable/1.6.x.
Bumped minimum Python version requirement to 2.7 in Django 1.7.
Removed some conditional code only needed under Python 2.6.