Handle WM_CHANGE_STATE requests for iconic state

http://tronche.com/gui/x/icccm/sec-4.html#s-4.1.4

 > IconicState - The client's top-level window is iconic (whatever that
 > means for this window manager). The client can assume that its
 > top-level window is not viewable, its icon_window (if any) will be
 > viewable and, failing that, its icon_pixmap (if any) or its
 > WM_ICON_NAME will be displayed.

For these requests, we just close the window.

fixes #1279

testcases/t/231-wm-change-state.t

@@ -0,0 +1,49 @@
+#!perl
+# vim:ts=4:sw=4:expandtab
+#
+# Please read the following documents before working on tests:
+# • http://build.i3wm.org/docs/testsuite.html
+#   (or docs/testsuite)
+#
+# • http://build.i3wm.org/docs/lib-i3test.html
+#   (alternatively: perldoc ./testcases/lib/i3test.pm)
+#
+# • http://build.i3wm.org/docs/ipc.html
+#   (or docs/ipc)
+#
+# • http://onyxneon.com/books/modern_perl/modern_perl_a4.pdf
+#   (unless you are already familiar with Perl)
+#
+# Correctly handle WM_CHANGE_STATE requests for the iconic state
+# See http://tronche.com/gui/x/icccm/sec-4.html#s-4.1.4
+# Ticket: #1279
+# Bug still in: 4.8-7-gf4a8253
+use i3test;
+
+sub send_iconic_state_request {
+    my ($win) = @_;
+
+    my $msg = pack "CCSLLLLLL",
+        X11::XCB::CLIENT_MESSAGE, # response_type
+        32, # format
+        0, # sequence
+        $win->id, # window
+        $x->atom(name => 'WM_CHANGE_STATE')->id, # message type
+        3, # data32[0]
+        0, # data32[1]
+        0, # data32[2]
+        0, # data32[3]
+        0; # data32[4]
+
+    $x->send_event(0, $x->get_root_window(), X11::XCB::EVENT_MASK_SUBSTRUCTURE_REDIRECT, $msg);
+}
+
+my $ws = fresh_workspace;
+my $win = open_window;
+
+send_iconic_state_request($win);
+sync_with_i3;
+
+is(@{get_ws($ws)->{nodes}}, 0, 'When a window requests the iconic state, the container should be closed');
+
+done_testing;