Use patch.patch() when checking for patch availability.
The test is closer to what we want to know. It also makes sense when you deal with patched versions of patch() as most people do under win32.
Basic install:
$ make # see install targets
$ make install # do a system-wide install
$ hg debuginstall # sanity-check setup
$ hg # see help
See http://www.selenic.com/mercurial/ for detailed installation
instructions, platform-specific notes, and Mercurial user information.