convert/gnuarch: keep track of original revision in extra headers
It seems to be standard to populate the .rev attribute of a commit
to keep track of original SCM revision names.
Just do it(tm).
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.