subrepo, hghave: use "svn --version --quiet" to determine version number
svn --version --quiet is implemented since svn 0.14.1 (August 2002)
and prints just the version number, not the long output (21 lines)
of "svn --version".
Additionally I expect this output format to be more stable, at least
it is not changed with different translations.
[ original upstream message ]