Roomserver perform join (#1001)

* Add PerformJoin template

* Try roomserver perform join

* Send correct server name to FS API

* Pass through content, try to handle multiple server names

* Fix local server checks

* Don't refer to non-existent error

* Add directory lookups of aliases

* Remove unneeded parameters

* Don't repeat join events into the roomserver

* Unmarshal the content, that would help

* Check if the user is already in the room in the fedeationapi too

* Return incompatible room version error

* Use Membership, don't try more servers than needed

* Review comments, make FS API take list of servernames, dedupe them, break out of loop properly on success

* Tweaks

federationsender/types/types.go

@@ -28,6 +28,12 @@ type JoinedHost struct {
 	ServerName gomatrixserverlib.ServerName
 }
 
+type ServerNames []gomatrixserverlib.ServerName
+
+func (s ServerNames) Len() int           { return len(s) }
+func (s ServerNames) Swap(i, j int)      { s[i], s[j] = s[j], s[i] }
+func (s ServerNames) Less(i, j int) bool { return s[i] < s[j] }
+
 // A EventIDMismatchError indicates that we have got out of sync with the
 // room server.
 type EventIDMismatchError struct {