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.
Mercurial
=========
Mercurial is a fast, easy to use, distributed revision control tool
for software developers.
Basic install:
$ make # see install targets
$ make install # do a system-wide install
$ hg debuginstall # sanity-check setup
$ hg # see help
Running without installing:
$ make local # build for inplace usage
$ ./hg --version # should show the latest version
See https://mercurial-scm.org/ for detailed installation
instructions, platform-specific notes, and Mercurial user information.