Improved the analysis of syntactic signatures

- collection of the number of untyed variables (because they need
  type variables) and adding corresponding type variables to the
  signature

- introduced 'Sign.t' into the analysis functions

- removed some unnecessary functions

	modified:   ocaml/class_table.ml
	modified:   ocaml/class_table.mli
	modified:   ocaml/context.ml
	modified:   ocaml/feature_table.ml
	modified:   ocaml/signature.ml
Added the pushing of contexts

	modified:   ocaml/context.ml
	modified:   ocaml/signature.ml