ctyp: added 'sorts' field;
may_insert_typ/term/env_sorts: observe Sign.all_sorts_nonempty;
may_insert_env_sorts: insert sorts of type subst only;
instantiate: insert sorts of insts;
tuned;
;;;
;;; $Id$
;;;
;;; Options for Proof General
;; Examples for sensible settings:
;(custom-set-variables '(isar-eta-contract nil))
;(custom-set-faces
; '(proof-locked-face
; ((((type x) (class color) (background light)) (:background "lightsteelblue2")))))