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
Mercurial
=========
Mercurial is a fast, easy to use, distributed revision control tool
for software developers.
Basic install:
$ make # see install targets
$ make install # do a system-wide install
$ hg debuginstall # sanity-check setup
$ hg # see help
Running without installing:
$ make local # build for inplace usage
$ ./hg --version # should show the latest version
See http://mercurial.selenic.com/ for detailed installation
instructions, platform-specific notes, and Mercurial user information.