hghave: detect cvs and cvsps availability
"cvsps -h" was returning 1 in cygwin, probably because CVSROOT was unset, which does not prevent it to work correctly.
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.