Work around problem where 'del os.environ["FOO"]' doesn't update environment.
test-hook failed since changeset 949516072388 because of this on Solaris 8.
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.