setup: replace runhg() with an hgcommand helper class Replace the runhg() function with an hgcommand helper class. hgcommand has as run() function similar to runhg(), but no longer requires the caller to pass in the exact path to python and the hg script, and the environment settings for invoking hg. For now this diff contains no behavior changes, but in the future this will make it easier for the hgcommand helper class to more intelligently figure out the proper way to invoke hg.