Thanks, I'll change that check to SERVER_SOFTWARE instead.. I was trying to avoid that one because it requires 2 checks, one for the variable and the second to ensure it begins with the string 'Google App Engine'... 

For CMS integration, your probably better off with my Joomla-GAE repository:
https://github.com/garyamort/joomla-gae/tree/overnumerousness

It also has the plugin needed for using the backend configuration ui.

Note: as it is not completed, all work is in the overnumeroussness branch. :-)  When I have a clean install process I'll merge things back to master and submit feature requests for the Joomla CMS tracker.

You can view various raw notes in the doc folder: https://github.com/garyamort/joomla-gae/tree/overnumerousness/doc

I'm using PHPStorm as my IDE and one really nice feature there is that if you start by creating a Google App Engine project and then merge the rest of the stuff in from git, you get all the idea settings properly configured to deploy to GAE as well as to execute things locally for testing.