Sean Farley <sean@farley.io> [Thu, 15 Jun 2017 17:13:23 -0700] rev 32919
hghave: add has_git_range for testing if git understands ext::sh
Even on CentOS 7, git is at version 1.8. It seems git 1.9 is when
ext::sh was introduced so we a check for that. The way these functions
are written follows the same style and format for the way we check svn
and bzr versions.