Reverts 5b2411bab704 and replaces it with a more general solution.
- works for both rpm and deb
- sidesteps eventual problems with local extensions that have nothing to do with
the build process (hg-git, for example, fails with version 4.4 because
ccf72242b638 removed peerrepository, and hg-git still uses it as of 0.8.9)
When bootstrapping a deb/rpm build, packagelib.sh starts performing a local
build for the sole purpose of parsing the output of "hg version".
Then it "hg archive"s the source code, and builds everything again.
For that initial step, we are perfectly good in using a pure python mercurial,
without compiling the c modules (base85, bdiff, zstdlib, ...).
On my personal system, this cuts down 22 seconds for a package build (the
bootstrapping build goes from ~30 to ~8 seconds).
Previously the -rc in our rc tags got dropped, meaning that those
packages looked newer to the packaging system than the later release
build. This rectifies the issue, though some damage may already have
been done on 3.6-rc builds.
I'm mostly cargo-culting the RPM version format - there don't appear
to be rules for RPM about how to handle this. Hopefully an RPM
enthusiast can fix up what I've done as a followup.
