Correctly restore focus after in-place restarts

Note: This change requires two in-place restarts when you are upgrading
in-place from an old version.

Fixes #611

testcases/t/188-regress-focus-restart.t

@@ -0,0 +1,34 @@
+#!perl
+# vim:ts=4:sw=4:expandtab
+#
+# Verifies that i3 survives inplace restarts with fullscreen containers
+#
+use i3test;
+
+my $tmp = fresh_workspace;
+
+open_window(name => 'first');
+open_window(name => 'second');
+
+cmd 'focus left';
+
+my ($nodes, $focus) = get_ws_content($tmp);
+is(scalar @$nodes, 2, 'two tiling nodes on workspace');
+is($nodes->[0]->{name}, 'first', 'first node name ok');
+is($nodes->[1]->{name}, 'second', 'second node name ok');
+is($focus->[0], $nodes->[0]->{id}, 'first node focused');
+is($focus->[1], $nodes->[1]->{id}, 'second node second in focus stack');
+
+cmd 'restart';
+sleep 1;
+
+does_i3_live;
+
+($nodes, $focus) = get_ws_content($tmp);
+is(scalar @$nodes, 2, 'still two tiling nodes on workspace');
+is($nodes->[0]->{name}, 'first', 'first node name ok');
+is($nodes->[1]->{name}, 'second', 'second node name ok');
+is($focus->[0], $nodes->[0]->{id}, 'first node focused');
+is($focus->[1], $nodes->[1]->{id}, 'second node second in focus stack');
+
+done_testing;