chgserver: import background server extension from cHg This extension is copied from https://bitbucket.org/yuja/chg/ -r 86feb5f2e971 It could be imported as mercurial/chgserver.py, but in that case, we would have to resolve circular import between chgserver and commandserver. So I decided to keep it as an extension. chgserver.chgcmdserver -> commandserver.server commandserver._servicemap -> chgserver.chgunixservice