Compatibility with IntelliJ 13 EAP

I made the following changes to allow the Leiningen plugin to work with IntelliJ 13.

I've been using it all day on the v13 EAP, and yet to see any problems.

If anyone wants a compiled version before this pull request gets merged and released, you can get it here:
https://dl.dropboxusercontent.com/u/16200445/intellij-leiningen-plugin.zip