Add Google App Engine Compatibility

[derekperkins]

I'm using the Google App Engine local dev environment and they use a goapp binary instead of the normal go binary, which includes their "appengine" packages to be referenced as if they were part of the standard library. If the "Go Installation" variable allowed for setting a binary as well as the path, that should make things work peachy. :)

https://developers.google.com/appengine/docs/go/tools/devserver#Go_Using_the_goapp_tool

[joefitzgerald]

The Go Installation preference is indeed an absolute path, but I look for it to end in go (https://github.com/joefitzgerald/go-plus/blob/master/lib/goexecutable.coffee#L41). Would be a simple fix to get past that.

[derekperkins]

I've never used coffeescript before, but would it be as simple as adding an or when looking for the executable name?

and goinstallation.lastIndexOf(path.sep + 'go') is goinstallation.length - 3 or and goinstallation.lastIndexOf(path.sep + 'goapp.bat') is goinstallation.length - 10

[derekperkins]

Sorry about my coffeescript issues with the PR. I can confirm that simply replacing the old Windows executable code with goinstallation.lastIndexOf(path.sep + 'goapp.bat') is goinstallation.length - 10 does work as expected.