Changed location of ffi.h header file for OSX based builds
Created originally on Bitbucket by amclean (Al McLean)
Changesets for this Pull Request have not been imported, because it had been already declined on Bitbucket. Marked as closed by the import user.
ffi.h does not exist in /usr/include/ffi.h on OSX Lion & Mountain Lion. This change allows the build script to pull it from the correct location : /usr/include/ffi/ffi.h