Minor Description
The new method __$swapInit was added (I think) to support reloading, enabling someone to drive re-initialization of some state (like constants, callsite arrays). Unfortunately it doesn't quite do that - with regards to the callsite array all it does is call $getCallSiteArray. This doesn't clear it, this just ensures it is initialized - and if initialized in the past it will not be reinitialized. This means the reloader has to additionally null the callsite array before calling __$swapInit - which is a shame since it is all invoked by reflection.