Merge in Symfony2 and PSR-0 autoloader

Since #1178246: Add Symfony2 HttpFoundation library to core is stalled, and we don't want to be blocked, I'm going to merge in the symfony2 code from that patch (it's a branch in the wscci repository anyway) and then convert our code to use namespaces. No sense waiting around for core to get its act in gear before we start writing code to where it will go in the end anyway.