coqc: accept -exclude-dir option (fix #3025)

git-svn-id: svn+ssh://scm.gforge.inria.fr/svn/coq/branches/v8.4@16433 85f007b7-540e-0410-9357-904b9bb8a0f7
Coqdep: add an -exclude-dir option (wish mentionned in #3025)

git-svn-id: svn+ssh://scm.gforge.inria.fr/svn/coq/branches/v8.4@16434 85f007b7-540e-0410-9357-904b9bb8a0f7