Introduce subpackages of 'foreign' for threaded and unthreaded cases.
Introduce subpackages of 'foreign' for threaded and unthreaded cases.

yallop/ocaml-ctypes,sjfloat/ocaml-ctypes,whitequark/ocaml-ctypes,fdopen/ocaml-ctypes,fdopen/ocaml-ctypes,sjfloat/ocaml-ctypes,yallop/ocaml-ctypes,whitequark/ocaml-ctypes,dsheets/ocaml-ctypes,fdopen/ocaml-ctypes,whitequark/ocaml-ctypes,ocamllabs/ocaml-ctypes,ocamllabs/ocaml-ctypes,dsheets/ocaml-ctypes,sjfloat/ocaml-ctypes,dsheets/ocaml-ctypes