Fix find_in_path not including some file extension logic under win32.
Windows shell resolves utility path by combining PATH, the utility name and a set of file extensions from PATHEXT.
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.