title: Does Ocaml OPAM detect prior installed Ocaml packages?
body: <p>I recently installed OPAM as per instructions to give it a try and it looks nice and I'd like to use it. However, it fails to detect previously installed OCAML packages that I installed manually before I choose to give OPAM a try. </p>
  
  <p>The first thing OPAM wants to do for any package installation now is to install ocamlfind. Querying for info about packages I installed manually do not reflect that they are already installed. This includes ocamlfind.</p>
  
  <p>I'm afraid to do anything as I have no idea what effect it might have to install another package. OPAM will overwrite or reinstall ocamlfind at the very least. Would this clobber my existing ocamlfind and its knowledge of all the packages I already manually installed and my ability to use them? I don't want to have to reinstall everything all over again. I've searched and searched but cannot find any documentation or forum posts about this precise topic and I don't know exactly how ocamlfind works under the hood.</p>
  
  <p>At the very least it would be nice if OPAM could either detect, or be told, which packages already exist and where they reside to avoid needless recompilation. Maybe it already does this but I've not been able to discover if it does.</p>