Fix bug# 2994, 2971 about better error messages.
Fix bug# 2956, porting fix from 8.4 branch


git-svn-id: svn+ssh://scm.gforge.inria.fr/svn/coq/trunk@16349 85f007b7-540e-0410-9357-904b9bb8a0f7
NMake*: avoid some warning about Let outside sections

git-svn-id: svn+ssh://scm.gforge.inria.fr/svn/coq/trunk@16350 85f007b7-540e-0410-9357-904b9bb8a0f7