adjust VM copyright notices to LGPL, use SCM_INTERNAL/API properly

adjust VM copyright notices to LGPL, use SCM_INTERNAL/API properly

* libguile/frames.c:
* libguile/frames.h:
* libguile/instructions.c:
* libguile/instructions.h:
* libguile/objcodes.c:
* libguile/objcodes.h:
* libguile/programs.c:
* libguile/programs.h:
* libguile/vm-bootstrap.h:
* libguile/vm-engine.c:
* libguile/vm-engine.h:
* libguile/vm-expand.h:
* libguile/vm-i-scheme.c:
* libguile/vm.c:
* libguile/vm.h: Update to use SCM_API and SCM_INTERNAL correctly. Adjust
  copyright to be the same as the copyright of Guile itself, which should
  be fine given that the FSF holds the whole thing.