Fix roots_enable_root_relative_urls logic and add local environment toggle

Bug:
It seems there is an error in the logic for the relative urls.  This caused some issues, ex:
![path-problem](https://f.cloud.github.com/assets/2755958/219330/7a2ab3aa-852a-11e2-9328-4208f1d305d4.png)

Improvement:
I also added an environment variable so that people don't make code changes on the production server... just something I think roots needs.