Taming the simpl evar hack that used to use negative evars.
Now we just generate evars in the given evar map.

At least, the test-suite isn't broken...

git-svn-id: svn+ssh://scm.gforge.inria.fr/svn/coq/trunk@16782 85f007b7-540e-0410-9357-904b9bb8a0f7