setup: explain to distutils how we write rc versions
When we use a rc version number (e.g. 4.8rc0), bdist_msi is using
distutils.StrictVersion to parse it into a tuple of numbers.
By default, StrictVersion.version_re only recognizes [ab] for alpha/beta,
where mercurial may use '-rc' or 'rc'.
This change makes StrictVersion parse correctly our version numbers, so that
bdist_msi doesn't fail on rc versions.
$ echo "[extensions]" >> $HGRCPATH
$ echo "mq=" >> $HGRCPATH
$ hg init
$ echo 'base' > base
$ hg ci -Ambase
adding base
$ hg qnew -mmqbase mqbase
$ hg qsave
$ hg qrestore 2
restoring status: hg patches saved state