Use findlib to decide the install directory

[vbgl]

The num library is no longer part of the standard library. As such, the install target of the Makefile should not attempt to install it in the directory that is dedicated to the standard library.

This patch lets findlib decide where to install the num library, according to user settings, as any other library.

BTW, the removal of the num library should be marked as “breaking” in the release notes of OCaml 4.06.

[gasche]

Well it was my understanding that installing num in the standard library directory was precisely meant to decrease incompatibilities -- for example to support people invoking ocaml nums.cma directly.

(I edited the OCaml Changes, thanks for the report)

[xavierleroy]

Why didn't I think of that and went through the pains of installing the files semi-manually?

This would break all existing code that links with Num without going through ocamlfind. In a couple of years we might do that, but not now.