* src/pexp.ml: Adjust to recent changes to Pinductive

* src/main.ml (process_typer_file.process_decl): Remove Lexp use since
it's not ready yet.

* src/pexp.ml (pexp_p_actual_arg, pexp_p_formal_arg)
(pexp_u_formal_arg): New functions.
(pexp_unparse, pexp_parse.pcases): Use them to handle the formal args
of inductive types.
(pexp_p_decls): Rename from pexp_decls.

* .gitignore: Ignore *.byte files.