Extraction AccessOpaque is now activated again by default (fix #2952)

git-svn-id: svn+ssh://scm.gforge.inria.fr/svn/coq/branches/v8.4@16316 85f007b7-540e-0410-9357-904b9bb8a0f7
Fix for bug #3004 (thanks Hugo !)

git-svn-id: svn+ssh://scm.gforge.inria.fr/svn/coq/branches/v8.4@16318 85f007b7-540e-0410-9357-904b9bb8a0f7