core: added scriptlet preparation support.

core: added scriptlet preparation support.

Added a prepare operation to scriptlet interpreter. If provided by an
interpreter, preparing a scriptlet should carry out any and all actions
necessary to finalize a compiled scriptlet for execution. For instance,
the simple builtin resolver scriptlet interpreter uses the preparation
phase to link function names to exported functions. The normal sequence
to run a scriptlet is now create - compile - prepare - execute.