keepalive: attempt to fix
issue1003
This is a reimport of the relevant piece of the upstream urlgrabber,
which appears to be more correct.
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.