Make fullscreen stacking respect EWMH

Fullscreen windows should only get their own layer when they have the input
focus. When they are unfocused they should be treated normally (FS#560).

Signed-off-by: Uli Schlachter <psychon@znc.in>

client.c

@@ -516,7 +516,7 @@ client_layer_translator(client_t *c)
     /* first deal with user set attributes */
     if(c->ontop)
         return LAYER_ONTOP;
-    else if(c->fullscreen)
+    else if(c->fullscreen && globalconf.screen_focus->client_focus == c)
         return LAYER_FULLSCREEN;
     else if(c->above)
         return LAYER_ABOVE;