Closure optimizations.

git-svn-id: svn+ssh://scm.gforge.inria.fr/svn/coq/trunk@16937 85f007b7-540e-0410-9357-904b9bb8a0f7
More sharing in Constr.map_with_binders.

git-svn-id: svn+ssh://scm.gforge.inria.fr/svn/coq/trunk@16938 85f007b7-540e-0410-9357-904b9bb8a0f7
Abstracting evar filter away. The API is not perfect, but better than nothing.

git-svn-id: svn+ssh://scm.gforge.inria.fr/svn/coq/trunk@16939 85f007b7-540e-0410-9357-904b9bb8a0f7