final (?) tweaks to the autocompile code

final (?) tweaks to the autocompile code

* libguile/load.c (do_try_autocompile): Use module_variable, not
  module_lookup, when resolving compile-file, so we get #f instead of an
  exception if the compiler is in the process of being loaded.
  (scm_primitive_load_path): In what I hope is the last patch to this
  code, recheck the fallback path if we found a stale installed .go file.