Added HAS_SERIAL to OSX configured flags
Added HAS_SERIAL to OSX configured flags

Not sure why I left these out. I considered the Mac to lack serial
ports, even though it's perfectly capable of using USB-to-serial
convertors. So it needs the support enabled by HAS_SERIAL to work under
muforth.

Welcome to the future!!

nickhen/muforth,nickhen/muforth