Crucible review CR-JRA-49 has some background info.

We now need to keep a registry of Actions in order to find them on the right classloader when we need to build them.
Currently we only register the "Simple" classname (ie without package information), because it was assumed that actions all live in the same package, but this is not true.
We need to handle different packages without name clashes, and also consider backward compatibility for plugins 1 Actions that did not specify a package name.