Alter the r1.35 of event.c race fix.  Remove the forward looking event
queue check (removing the need for a server grab/ungrab) - if the client
is going away, let it fall all the way through to a DestroyNotify event.
There's no longer a need for us to manually destroy a client ourselves
(removing yet another server grab/ungrab).  Instead, when the
UnmapNotify event is synthetic, simply set the state to Withdrawn (as
per ICCCM), else Iconic (in our case 'hidden').

Verified with test case from the 2009 race which was the original reason
for r1.35 of event.c.