layout restore: create and render placeholder windows

This is not entirely done yet, but TODO entries are placed in the code
where appropriate.

include/restore_layout.h

@@ -0,0 +1,32 @@
+/*
+ * vim:ts=4:sw=4:expandtab
+ *
+ * i3 - an improved dynamic tiling window manager
+ * © 2009-2013 Michael Stapelberg and contributors (see also: LICENSE)
+ *
+ * restore_layout.c: Everything for restored containers that is not pure state
+ *                   parsing (which can be found in load_layout.c).
+ *
+ */
+#ifndef I3_RESTORE_LAYOUT_H
+#define I3_RESTORE_LAYOUT_H
+
+/**
+ * Opens a separate connection to X11 for placeholder windows when restoring
+ * layouts. This is done as a safety measure (users can xkill a placeholder
+ * window without killing their window manager) and for better isolation, both
+ * on the wire to X11 and thus also in the code.
+ *
+ */
+void restore_connect(void);
+
+/**
+ * Open placeholder windows for all children of parent. The placeholder window
+ * will vanish as soon as a real window is swallowed by the container. Until
+ * then, it exposes the criteria that must be fulfilled for a window to be
+ * swallowed by this container.
+ *
+ */
+void restore_open_placeholder_windows(Con *con);
+
+#endif