Moved code from Pretype_error to Evarutil

git-svn-id: svn+ssh://scm.gforge.inria.fr/svn/coq/trunk@16194 85f007b7-540e-0410-9357-904b9bb8a0f7
Splitted Evarutil in two files

git-svn-id: svn+ssh://scm.gforge.inria.fr/svn/coq/trunk@16195 85f007b7-540e-0410-9357-904b9bb8a0f7