new package for labltk and ocamlbrowser, since they split from ocaml
new package for lablgtk 2.18.2
only install labltk on 4.02 and above
add libconfig1-dev as external dependency
replace libconfig1-dev by libexpat1-dev
Merge pull request #2722 from garrigue/master

new package for labltk and ocamlbrowser, since they split from ocaml