Made OptiPNG & JPEGTrans binary for OSX executable

@skspk - OSX Build was failing to optimize, had to make the osx binaries executable to run. All good now, and nice idea with the layout!

Just one thing (for the future) - Yeoman have created these modules as NPM Modules if it is easier to link up etc:
https://github.com/yeoman/node-jpegtran-bin
https://github.com/yeoman/node-optipng-bin

Nice job :+1: