Don't propagate RUBYOPT to MacRuby script

On my machine, bundler sets it and then tries to launch the MacRuby script and hilarity ensues and it doesn't work.
Add monkey patch to workaround posix-spawn bug

When trying to rohanify http://celebslists.com/images/bette-midler/bette-midler.jpg, I reliably hit an issue where posix-spawn tries to call `close` on a nil file handle. This seems to fix it.
Merge pull request #1 from scottjg/fixes

Various fixes to get this thing working