To be able to use the exact same version in both upstream tarballs
and downstream packages always use dot as a version separator.

This enables downstream packages to re-use the upstream versions
(especially the pre-release ones which no longer contain dash) when
building packages. This is very useful for building testing packages
e.g. in Fedora and Arch, which do not allow dash in version number.

Tags should follow this format from now on as well, e.g. 2.99.0.alpha
instead of 2.99.0-alpha