add experimental freebsd support

Don't know if this has come up before, but I have a need to use GeoIP on FreeBSD. Added it to the os array and ran the tests.

Got 113 passing and 2 pending (not sure what the "pending" means) in terms of this package.

This was with the GeoIP-1.6.3_1 pkgng package on FreeBSD 10.1-RELEASE.

I am willing to be the contact for FreeBSD testing and issues going forward. I use GeoIP heavily on C++ and now on Node.js.