doc/Makefile: ensure C locale
The man pages can actually be translated by building them in a
different locale. However, the man pages contain internal links to
certain sections, and when the section titles are translated, the
links change too. So it is currently not recommended to build the man
pages in anything by the "C" locale.
Basic install:
$ make # see install targets
$ make install # do a system-wide install
$ hg debuginstall # sanity-check setup
$ hg # see help
See http://mercurial.selenic.com/ for detailed installation
instructions, platform-specific notes, and Mercurial user information.