Fix Makefile for OSX

This fixes an issue with the Makefile caused by the version of sed that ships with OSX. It does rely on uname existing, but I think that's fair considering the platforms ncurses itself is available for.
Re-suppress sed command echo
Use zero-length argument to sed instead of -e
Merge pull request #51 from pmsanford/osx-makefile

Fix Makefile for OSX