frame, program, objcode, etc inits use load-extension

frame, program, objcode, etc inits use load-extension

* libguile/extensions.h: Define a scm_t_extension_init_func.

* libguile/frames.c:
* libguile/instructions.c:
* libguile/objcodes.c:
* libguile/programs.c:
* libguile/vm.c: Register extension init funcs. Should play nicer with a
  static Guile, in addition to working on Darwin with non-default
  installation prefixes without munging DYLD_LIBRARY_PATH.

* module/system/vm/frame.scm:
* module/system/vm/instruction.scm:
* module/system/vm/objcode.scm:
* module/system/vm/program.scm:
* module/system/vm/vm.scm: Use load-extension.