* Factor out functions for injecting events into database
I want to add some more flexibility to the tools for injecting events into the
database, and I don't want to clutter up HomeserverTestCase with them, so let's
factor them out to a new file.
* Rework TestReplicationDataHandler
This wasn't very easy to work with: the mock wrapping was largely superfluous,
and it's useful to be able to inspect the received rows, and clear out the
received list.
* Fix AssertionErrors being thrown by EventsStream
Part of the problem was that there was an off-by-one error in the assertion,
but also the limit logic was too simple. Fix it all up and add some tests.
A couple of weird caveats:
* If we can't validate your macaroon, we fall back to checking that
your access token is in the DB, and ignoring the failure
* Even if we can validate your macaroon, we still have to hit the DB to
get the access token ID, which we pretend is a device ID all over the
codebase.
This mostly adds the interesting code, and points out the two pieces we
need to delete (and necessary conditions) in order to fix the above
caveats.
