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.