Needed to split into 2 conditional spans for grammar reason

Conflicts:
	synapse/http/client.py

Add support for registering with a threepid to the HS (get credentials from the client and check them against an ID server).

Normalise users power levels so that the user with the higher power level will have a bar covering 100% of the width of his avatar

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

Add exception handling to directory servlet, so we don't 500. Mark directory API as volatile in the api docs.

Fix up directory server to not require uploading room hosts. Update the room hosts table with the current room hosts (if we have them) on GET.

... key from all the Presence messages

Make retrying requests on DNS failures configurable, and turn off retrying only in directory.get_association

Do not define power level limits in setUserPowerLevel. Update the function to be used as a resetUserPowerLevel