tests: have dumbhttp.py use cmdutil.service() to wait for child to listen() Because the original dumbhttp.py exited without waiting for listen(), several tests could fail with "abort: error: Connection refused" if subsequent hg command is fast enough.

test-revert: remove obsolete comment about known misbehavior It seems like the last known misbehvior that the comment was referring to was dealt with in 2ff28e07d7d6 (revert: properly back up added files with local modification, 2014-08-31).