Allow expressions as constructor names and inductive type refs

* src/lexp.ml (lexp): Allow an lexp for the inductive type arg of Cons.
(lexp_unparse): Adjust accordingly.
(push_susp): Adjust accordingly.  Also merge fix from unification branch.

* src/lparse.ml (_lexp_p_infer): Adjust to new Pcons and Cons
(lexp_get_inductive_type): Remove.
(lexp_read_pattern): Adjust to new Ppatcons.

* src/opslexp.ml (conv_p', check): Adjust to new Cons.

* src/pexp.ml (ppat): Allow any exp as constructor.
(pexp): Allow an exp for the inductive type arg of Cons.