fixing bug in component.py where the visibility of overlays and underlays were not being checked, and the invisible_layout trait was not being respected.  (thanks to Mike at BAE for the bug report)
fixing bug in component.py where the visibility of overlays and underlays were not being checked, and the invisible_layout trait was not being respected.  (thanks to Mike at BAE for the bug report)

tommy-u/enable,tommy-u/enable,tommy-u/enable,tommy-u/enable