bugfix: don't set input focus if not accepted

Long description:

http://tronche.com/gui/x/icccm/sec-4.html#s-4.1.7

> Clients using the Globally Active model can only use a SetInputFocus request
> to acquire the input focus when they do not already have it on receipt of one
> of the following events:
> * ButtonPress
> * ButtonRelease
> * Passive-grabbed KeyPress
> * Passive-grabbed KeyRelease

Since managing a window happens on a MapNotify (which is absent from this
list), the window cannot accept input focus, so we should not try to focus
the window at all.

Fixes an issue with xfce4-notifyd which (correctly) declines focus when
we send WM_TAKE_FOCUS, which puts i3 in a state where i3 focus and X
focus are different when a notification appears.

To apply this patch, use:
curl http://cr.i3wm.org/patch/584/raw.patch | git am

@@ -505,7 +505,7 @@ void manage_window(xcb_window_t window, xcb_get_window_attributes_cookie_t cooki

     /* Defer setting focus after the 'new' event has been sent to ensure the

      * proper window event sequence. */

-    if (set_focus) {

+    if (set_focus && !nc->window->doesnt_accept_focus) {

         DLOG("Now setting focus.\n");

         con_focus(nc);

     }

@@ -59,6 +59,18 @@ subtest 'Window without WM_TAKE_FOCUS', sub {

     done_testing;

 };

+# http://tronche.com/gui/x/icccm/sec-4.html#s-4.1.7

+# > Clients using the Globally Active model can only use a SetInputFocus request

+# > to acquire the input focus when they do not already have it on receipt of one

+# > of the following events:

+# > * ButtonPress

+# > * ButtonRelease

+# > * Passive-grabbed KeyPress

+# > * Passive-grabbed KeyRelease  

+#

+# Since managing a window happens on a MapNotify (which is absent from this

+# list), the window cannot accept input focus, so we should not try to focus

+# the window at all (right?)

 subtest 'Window with WM_TAKE_FOCUS and without InputHint', sub {

     fresh_workspace;

@@ -74,7 +86,7 @@ subtest 'Window with WM_TAKE_FOCUS and without InputHint', sub {

     $window->map;

-    ok(recv_take_focus($window), 'got ClientMessage with WM_TAKE_FOCUS atom');

+    ok(!recv_take_focus($window), 'did not receive ClientMessage');

     done_testing;

 };