webdav: Fix interpretation of client cert properties

Addresses a problem that causes the interpretation of the
webdavWantClientAuth and webdavNeedClientAuth properties to
be reversed.

JGlobus 2 seems to have a different interpretation of these
flags. The relevant JGlobus code is:

	 if (this.requireClientAuth.booleanValue() == Boolean.TRUE) {
             this.sslEngine.setNeedClientAuth(this.requireClientAuth.booleanValue());
	 } else
             this.sslEngine.setWantClientAuth(!this.acceptNoClientCerts.booleanValue());

Target: trunk
Request: 2.6
Request: 2.2-sha2
Require-notes: yes
Require-book: no
Acked-by: Tigran Mkrtchyan <tigran.mkrtchyan@desy.de>
Patch: http://rb.dcache.org/r/5615/
(cherry picked from commit c914cdcb1fa4d476a8eaeb7abc103251c065170b)