* The interface now gives the user the possibility of (re-)opening an existing
constant.
* Tactic Elim no more exposed in the user interface. Replaced by ElimIntros.
* Selection of subterms in the hypothesis of the goal is now "sound".
* Reduction tactics (Whd, Reduce, Simpl) now work also on the hypothesis.
New bug/feature: their changes are lost when moving to another goal
and coming back afterwards.