git-svn: test for creating new directories over svn://

git-svn: test for creating new directories over svn://

As reported by Matthieu Moy, this is causing svnserve to
terminate connections, because it segfaults.

This test is disabled by default and can be enabled by setting
SVNSERVE_PORT to an unbound (for 127.0.0.1) TCP port in the
environment (in addition to SVN_TESTS=1).  I'm not comfortable
with having a test start a daemon by default and take up a port
that could potentially stay running if the test failed.

Signed-off-by: Eric Wong <normalperson@yhbt.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>