+ * Closes the given container including all children.
+ * Returns true if the container was killed or false if just WM_DELETE was sent
+ * and the window is expected to kill itself.
+ *
+ * The dont_kill_parent flag is specified when the function calls itself
+ * recursively while deleting a containers children.
+ *
+ * The force_set_focus flag is specified in the case of killing a floating
+ * window: tree_close_internal() will be invoked for the CT_FLOATINGCON (the parent
+ * container) and focus should be set there.