In opencv 2.x, unfree libraries are built by default. The package
should therefore have been marked as unfree, but wasn't.
I've disabled the non-free libraries by default, and added an option
to enable them. There are three programs in Nixpkgs that depend on
opencv2: mathematica, pfstools, and p2pvc. pfstools requires the
non-free libraries if it's built with opencv support, so I've disabled
opencv by default there and added an option to enable it. p2pvc links
fine, so presumably doesn't need the non-free libraries. I can't test
mathematica, so I'm just going to leave it alone.
d69583c6c2