Readded manifest.xml file to not break rFSM for fuerte and earlier

This pull request re-adds the `manifest.xml` that has been removed in 6bee1ada36c3b1fafb24f28a5774062d62723c95.
It is required for older ROS releases (fuerte and earlier).

See http://lists.mech.kuleuven.be/pipermail/orocos-dev/2014-February/012797.html.