Revert "Don't call "focus" hook in client_focus()"

This reverts commit 27f9c0177a.

This commit broke code like the following because reading client.focus would
still return the previously focused client:

awful.client.focus.byidx(1)
if client.focus then client.focus:raise() end

objects/client.c

@@ -418,6 +418,9 @@ client_focus(client_t *c)
     /* X11 doesn't let you focus a window that isn't viewable */
     client_unban(c);
 
+    if (!c->nofocus)
+        client_focus_update(c);
+
     client_set_focus(c, !c->nofocus);
 }