Withoug a proper implementation of DetermineClientCmd, clients that
connect via an ssh tunnel are miscategorized as local.  This results
in failures when we try to use SCM_RIGHTS (eg: in MIT-SHM).

Fixes: https://github.com/XQuartz/XQuartz/issues/314


Signed-off-by: Jeremy Huddleston Sequoia <jeremyhu@apple.com>