revert commit 14719

git-svn-id: http://caml.inria.fr/svn/ocaml/trunk@14723 f963ae5c-01c2-4b8c-9fe0-0dff7051ff02
* Do not require cmi file to be present if module alias is not accessed
  (using -trans-mod)
* Add warning 49 for that case; use same warning in place of deprecated
  for Env.scrape_alias


git-svn-id: http://caml.inria.fr/svn/ocaml/trunk@14724 f963ae5c-01c2-4b8c-9fe0-0dff7051ff02