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

Don't eat federation transmit errors during unit tests; fix remote presence EDU-sending test because of this

apidocs: Tweak join response format. Explicitly state empty JSON objects where they are required by the spec. Mark unimplemented room GET APIs clearly.

Conflicts:
	synapse/http/server.py
        synapse/http/content_repository.py

Edited /presence REST servlet to raise SynapseErrors to return a standard error response, rather than a string.

Better indicate in the page feedback section that a user can't join a room (because he has been banned for ex). May be worth to be put in the middle of screen