[wg-windows] Interim solution for OPAM on Windows

[Jonathan Protzenko]

Hi all,

David's email reminded me that I forgot to tell the world about this 
horrible hack that I did a while ago.

http://protz.github.io/ocaml-installer/ now offers an installer with 
OPAM. The toolchain is the usual one (native compilers / generating 
native windows programs / using mingw64 32-bit compilers). However, the 
installer now installs an "opam" program in c:\ocaml\bin. The opam 
program is a *cygwin 32-bit binary*, so it only works within a cygwin 
32-bit terminal. I got as far as doing "opam init" and "opam install 
a-whole-bunch-of-packages", including mezzo and all its dependencies, 
batteries, and a couple others.

All in all, I hope it'll provide a good enough interim solution until 
David finishes everything and I can, eventually, retire my installer :).

Caveats:
- there is a massive dependency on cygwin now as your build + opam 
environment;
- that won't help with "sophisticated" packages (e.g. openssl, lablgtk) 
because afaik, you still have to fight to install and compile the gtk / 
openssl libraries yourself on windows;
- I don't expect opam switch to work at all... it wouldn't make much 
sense anyhow.

Feedback is welcome.

Cheers,

Jonathan