- install evar printer for debugging
- make unification try canonical structures before expansion as in evar_conv
- add a fast path to evar inversion (patch from B. Ziliani).


git-svn-id: svn+ssh://scm.gforge.inria.fr/svn/coq/trunk@16945 85f007b7-540e-0410-9357-904b9bb8a0f7