This caused `prev_state_ids` to be incorrect if the state event was not
replacing an existing state entry.

... and use it in places where it's trivial to do so.

This will make it easier to pass room versions into the FrozenEvent
constructors.

I'm going to need another copy (hah!) of this.

Broadly three things here:

* disable W504 which seems a bit whacko
* remove a bunch of `as e` expressions from exception handlers that don't use
  them
* use `r""` for strings which include backslashes

Also, we don't use pep8 any more, so we can get rid of the duplicate config
there.

Also make it an inclusive not exclusive filter, as the spec demands.

Have all unit tests import from our own subclass of trial's unittest TestCase; set up logging in ONE PLACE ONLY

fix the copyright holder from matrix.org to OpenMarket Ltd, as matrix.org hasn't been incorporated in time for launch.

add in copyrights to everything, not just the synapse subdir, and add a copyrighter.pl whilst we're at it