Refactorings to apply-hook and push-continuation-hook

Refactorings to apply-hook and push-continuation-hook

* libguile/vm-engine.c (vm_engine): Always invoke the apply hook after
  the ip has been reset.  Avoids problems in frame-bindings, which
  builds its bindings map based on the IP.  Invoke push-continuation
  before linking the new frame, so that more locals are available to the
  frame inspector.

* module/system/vm/traps.scm (trap-in-procedure): No need for a
  push-cont handler, as the apply handler will exit the frame.