Rewrite active/inactive client handling in client_setactive();
client_leave() served no real purpose, likewise no reason to handle
LeaveNotify events since an EnterNotify will process the next active
client (and we don't have anything important to process anyway), so
xev_handle_leavenotify() goes as well.  Allows a simplification of
client_mtf() and client_cycle_leave() for clarity.  While here, unify a
few client_current() checks.

No intended behaviour change.
simplify/unfold
Remove the option to bind a key by keycode with brackets; it never
worked (and no one complained!).  While it's fairly easy to fix, users
should be using keysym names and not keycodes.

Discussed at length months ago with todd@, matthieu@ and Owain.
alter -r1.145 getsizehints to deal with clients that don't have
WM_NORMAL_HINTS.
like gap, make snapdist per screen