Added *.pig.substituted files to be recognized as pig files in ST2

I make substituted files often, and wanted them to be recognized as Pig files in Sublime Text. I made the change to make it so. Feel free to merge if you like it.

Also, thanks for your changes to the original chrislongo/Pig project. It's nice to be able to comment and uncomment lines.

Have you considered submitting a pull request to the original project to make it easier to get your changes into the version of the Apache Pig package in the Package Repository?

Thanks again!

JT