Force joining by alias to go through the send_membership_event checks,
rather than bypassing them straight into _do_join. This is the first of
many stages of cleanup.

This reverts commit cf81375b.

It subtly violates a guest joining auth check

Merge two of the room join codepaths

There's at least one more to merge in.

Side-effects:
 * Stop reporting None as displayname and avatar_url in some cases
 * Joining a room by alias populates guest-ness in join event
 * Remove unspec'd PUT version of /join/<room_id_or_alias> which has not
   been called on matrix.org according to logs
 * Stop recording access_token_id on /join/room_id - currently we don't
   record it on /join/room_alias; I can try to thread it through at some
   point.

There's at least one more to merge in.

Side-effects:
 * Stop reporting None as displayname and avatar_url in some cases
 * Joining a room by alias populates guest-ness in join event
 * Remove unspec'd PUT version of /join/<room_id_or_alias> which has not
   been called on matrix.org according to logs
 * Stop recording access_token_id on /join/room_id - currently we don't
   record it on /join/room_alias; I can try to thread it through at some
   point.

Catch the exceptions thrown by twisted when you write to a closed con…

Enforce user_id exclusivity for AS registrations

This whole set of checks is kind of an ugly mess, which I may clean up
at some point, but for now let's be correct.

Return events in correct order for /events

Improvements to initial /syncs

This helps to ensure we don't completely starve other requests.

Don't bother copying records on parent context

	Atomically persit push actions when we persist the event

Update documentation

Derive macaroon_secret_key from signing key.