Support _NET_WM_USER_TIME.

With this patch, we support the special value "0" for _NET_WM_USER_TIME
on a window upon managing it, which indicates that the window shall not
be focused.

fixes #2064

testcases/t/259-net-wm-user-time.t

@@ -0,0 +1,74 @@
+#!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)
+#
+# Test for _NET_WM_USER_TIME.
+# Ticket: #2064
+use i3test;
+use X11::XCB 'PROP_MODE_REPLACE';
+
+my ($ws, $other, $con);
+
+sub open_window_with_user_time {
+    my $wm_user_time = shift;
+
+    my $window = open_window(
+        before_map => sub {
+            my ($window) = @_;
+
+            my $atomname = $x->atom(name => '_NET_WM_USER_TIME');
+            my $atomtype = $x->atom(name => 'CARDINAL');
+            $x->change_property(
+                PROP_MODE_REPLACE,
+                $window->id,
+                $atomname->id,
+                $atomtype->id,
+                32,
+                1,
+                pack('L1', $wm_user_time),
+            );
+        },
+    );
+
+    return $window;
+}
+
+#####################################################################
+# 1: if _NET_WM_USER_TIME is set to 0, the window is not focused
+#    initially.
+#####################################################################
+
+$ws = fresh_workspace;
+
+open_window;
+$other = get_focused($ws);
+open_window_with_user_time(0);
+
+is(get_focused($ws), $other, 'new window is not focused');
+
+#####################################################################
+# 2: if _NET_WM_USER_TIME is set to something other than 0, the
+#    window is focused anyway.
+#####################################################################
+
+$ws = fresh_workspace;
+
+open_window;
+$other = get_focused($ws);
+open_window_with_user_time(42);
+
+isnt(get_focused($ws), $other, 'new window is focused');
+
+done_testing;