mod_dav_svn requires authn to be enabled for locking to be possible. If one
attempts to lock with anonymous access then mod_dav_svn returns 401
HTTP_UNAUTHORIZED. With 1.8 the client reports
svn: warning: W120190: Error running context: An error occurred during
which doesn't give much of a clue as to the problem.
With 1.7/neon the client reports
svn: E175002: Server sent unexpected return value (401 Authorization Required)
in response to LOCK request for '/obj/repo/A/f'
which, although not great, is better as it includes both the 401 and the path.