Native Namespace Code Prep

This PR adds in the root namespace backslash on calls to internal PHP and SPL classes. This will facilitate the platform moving to native PHP namespaces, whenever that may be.

More info can be found here: http://www.php.net/manual/en/language.namespaces.faq.php#language.namespaces.faq.globalclass

Also, I've replaced some explicit calls to class names with `__CLASS__` in callables. For example, in `JLoader` when calling `spl_autoload_register()`. Also, where creating a new instance of the containing class, I've changed `new JClassName` to `new static`. I've not completed all instances of these yet.

This PR does not break B/C at all, as the whole codebase is already operating in the root/global namespace. But this will need to be done when we do move to namespaces, so I thought I could help that along.

No unit tests were harmed in the making of this pull request.