build: don't clean __version__.py on 'make clean' in release tarballs When running 'make clean' in an extracted release tarball, file mercurial/__version__.py is removed, causing a subsequent install to indicate 'version unknown'. This problem was reported in the past [1] and a patch proposed in that mail, but was never properly sent nor applied. [1] http://selenic.com/pipermail/mercurial/2010-December/036249.html