Fix bug #3561, correct folding of env in context[] matching.
Revert "Ltac's [idtac] is now interpreted outside of a goal if possible."

This reverts commit afa441019432f70245fed6adc5eb0318514e4357.
Revert "Ltac's idtac is now implemented using the new API."

This reverts commit 5b92ff7b0a641bf2daa31b60bf49b57a5d1e8452.
Revert "Tacinterp: [interp_message] and associate now only require an environment rather than an entire goal."

This reverts commit 4eaafcd00992302c186b8d11e890616726ebd822.
Revert "Tactics: [tclENV] is now sensitive to [Proofview.Goal.enter]."

This reverts commit 664b3cba1e8d326382ca981aa49fdf00edd429e6.

Conflicts:
	proofs/proofview.ml
Using goal-tactics to interpret arguments to idtac.

This allows to write a multigoal idtac without having to resort to
the hack of modifying the global environment tactic through tclIN_ENV,
which may cause trouble if we want to modify it in a state-passing style.