`updatePendingEvent` doesn't emit oldEventId to 'Room.localEchoUpdated' event.

Nobody has claimed this yet.

I have a situation that when I send a message using `sendMessage`, matrix client returns a matrix event with a temporary event id, the `Room.localEchoUpdated` gets fired when the message changing its status from `sending` to `sent`, however, I won't be able to get the temporary event id from `Room.localEchoUpdated`, that is, there is no way to connect the changed event.

Based on the matrix-js-sdk doc, the third parameter of [MatrixClient"Room.localEchoUpdated"](http://matrix-org.github.io/matrix-js-sdk/0.9.2/module-client.html#~event:MatrixClient%2522Room.localEchoUpdated%2522) should be oldEventId. However this line of code emits the newEventId since `event.getId()` returns the newEventId instead of the old one.
https://github.com/matrix-org/matrix-js-sdk/blob/4153845346c0d8ab087e0e6e854f6f75d744af6d/src/models/room.js#L820

I am not so sure whether it returns the `event.getId()` on purpose, if not, I can create a pr and fix this issue.

Thanks in advance.

Start in src/models/room.js at the updatePendingEvent code linked in the issue, and inspect how Room.localEchoUpdated is emitted when a temporary event becomes sent. Confirm that the event reports the old temporary event ID rather than event.getId(); done means callers can connect the changed event to its temporary ID.

Written by the indexing model from the issue text.