Checkpoint: save VERSION so that I can test make_dist_tarball
Remove references to SVN and Mercurial.
Remove distscript.sh references to SVN; use "git describe" to get the version.
Update to new Trac URL in a hwloc_pkg.m4 comment.
Use new VERSION scheme for hwloc_get_version.sh
Update make_dist_tarball to use git instead of svn.

Use the new VERSION number scheme, and enforce that this script will
not be used for making snapshot tarballs.
Rename create_tarball.sh -> make_snapshot_tarball, and adapt to using
git instead of SVN.
No need for update-my-copyright.pl to work with hg or SVN any more.
Update hwloc.doxy (i.e., README) SVN references to git.