X.H.ServerMode: Only read the first ClientMessage data item

Atoms are at most 32-bit even on 64-bit platforms, per the X protocol,
despite them being stored in a CLong. Even if they weren't (and they
are, see /usr/include/X11/Xproto.h and
https://stackoverflow.com/a/23265984/3407728), xmonadctl isn't unpacking
the CLong into multiple data items.

XMonad/Hooks/ServerMode.hs

@@ -93,7 +93,7 @@ serverModeEventHookF key func (ClientMessageEvent {ev_message_type = mt, ev_data
         d <- asks display
         atm <- io $ internAtom d key False
         when (mt == atm && dt /= []) $ do
-         let atom = fromIntegral $ toInteger $ foldr1 (\a b -> a + (b*2^(32::Int))) dt
+         let atom = fromIntegral (head dt)
          cmd <- io $ getAtomName d atom
          case cmd of
               Just command -> func command