Forbid non-ASes from registering users whose names begin with '_'

Handle the case of missing auth events when joining a room

Create separate methods for getting messages to push

for the email and http pushers rather than trying to make a single
method that will work with their conflicting requirements.

The http pusher needs to get the messages in ascending stream order, and
doesn't want to miss a message.

The email pusher needs to get the messages in descending timestamp order,
and doesn't mind if it misses messages.

Comment get_unread_push_actions_for_user_in_range function

Add some basic admin API docs

Fix retry utils to check if the exception is a subclass of CME

Send the correct host header when fetching keys

Don't include name of room for invites in push

Avoids insane pushes like, "Bob invited you to invite from Bob"

Add r0.2.0 to the "supported versions" list

Make the device id on e2e key upload optional

1. Add v2_alpha URL back in, since things seem to be using it.

2. Don't reject the request if the device_id in the upload request fails to
   match that in the access_token.

Clean up verify_json_objects_for_server

Conflicts:
	synapse/crypto/keyring.py

Add a couple more checks to the keyring

Fix a couple of bugs in the transaction and keyring code