ocp-build: implemented a simple -install-lib option

ocp-build -install-lib LIBDIR  PACKAGES
  will install all library files of PACKAGES in LIBDIR (usually, something
   like /usr/lib/ocaml), generating META files.
ocp-build -install-lib - PACKAGES
  does the same, but LIBDIR is set to OCAMLLIB from ocamlc

if PACKAGES is empty, the action is done for all packages.