Changing the type of Ltac values. Now they are toplevel generic
arguments. That way we will be able to define interpretation of
tactics without referring to tactic values.

Quite ad-hoc for now.

git-svn-id: svn+ssh://scm.gforge.inria.fr/svn/coq/trunk@16574 85f007b7-540e-0410-9357-904b9bb8a0f7
Added Genarg as generic argument type.

git-svn-id: svn+ssh://scm.gforge.inria.fr/svn/coq/trunk@16575 85f007b7-540e-0410-9357-904b9bb8a0f7
Totally replaced ad-hoc tactic values by generic arguments. Now
only tactics results are special tactic values represented by
the non-exported tacvalue type.

git-svn-id: svn+ssh://scm.gforge.inria.fr/svn/coq/trunk@16576 85f007b7-540e-0410-9357-904b9bb8a0f7
Moving coercion functions out of Tacinterp.

git-svn-id: svn+ssh://scm.gforge.inria.fr/svn/coq/trunk@16577 85f007b7-540e-0410-9357-904b9bb8a0f7