This involves making PhysicsActor.PIDActive get as well as set.
On physics components that don't implement this (all characters and some phys engines) we return false.
This was an oversight when removing some race conditions from PhysicsActor setting recently.
Regression tests extended to probe this code path.
Extending regression tests required implementation of a BasicPhysicsPrim (there was none before). However, BasicPhysics plugin is still of no current practical use other than to fill in as a component for other parts of regression testing.
