revert: be more helpful on uncommitted merges BEFORE: $ hg revert abort: no files or directories specified (use --all to discard all changes) AFTER: $ hg revert abort: no files or directories specified (uncommitted merge, use --all to discard all changes, or 'hg update -C .' to abort the merge)

opener: add self._audit (issue2862)

cmdserver: write the hello message as one chunk on the 'o' channel This is a guaranteed by the protocol: clients know they need to read one chunk off of the 'o' channel and treat that as the hello message. They should ignore fields they don't recognize so they stay compatible with new versions of the server in case we decide to add something.