Renaming goal-entering functions.

1. Proofview.Goal.enter into Proofview.Goal.nf_enter.
2. Proofview.Goal.raw_enter into Proofview.Goal.enter.
3. Proofview.Goal.goals -> Proofview.Goals.nf_goals
4. Proofview.Goal.raw_goals -> Proofview.Goals.goals
5. Ftactic.goals -> Ftactic.nf_goals
6. Ftactic.raw_goals -> Ftactic.goals

This is more uniform with the other functions of Coq.
Fixing clearbody : typecheck definitions in context.
Adding a way to inject tactic closures in interpretation values.
Proper interpretation function for tauto.

Instead of passing glob tactics through the infamous globTacticIn hack and
antiquotation feature of the Ltac syntax, we put them in the interpretation
environment as closures. This should be used everywhere to get rid of this
buggy antiquotation syntax.

This fixes bug #2800.
Code simplification in Tacinterp.
Inlining code in Tacinterp that was only used once.