Support for Server Specified Database and Configuration Settings

[populist]

There are many different Drupal development and hosting platforms that would like to inject their settings into a Drupal installation without formally writing it to the settings.php.

This pull request allows this through a $_SERVER['SERVER_SETTINGS'] value that can be injected in a variety of ways. This is the method we have used at Pantheon to inject our settings for years, but would love for it to be more cleanly supported in Backdrop.

Reference: backdrop/backdrop#60

[quicksketch]

I'd like to make sure we get this into 1.0.0. I'll try to take on the old PR, update for the latest APIs, and then build out some basic tests for it.

[populist]

I think that would be great. It would be great to have Backdrop running on Pantheon without the clunky patch to bootstrap.inc that we need to do for Drupal sites.

[quicksketch]

Doh, apparently I made a new issue for this. However, it's now done. :)

Fixed in #281.