Cleanup in rewrite.ml4, remove Evd.merge... replaced by an evars_reset_evd 
(to push the metas from a clenv into the current evars).



git-svn-id: svn+ssh://scm.gforge.inria.fr/svn/coq/trunk@16568 85f007b7-540e-0410-9357-904b9bb8a0f7