ajaxlib: MDL-16695 New page_requirements_manager class. Soon to replace require_js.
This new class does the work that require_js used to do, and more.
It can track a number of different things that may be required to
be output somewhere on the page, including:
* Links to JS files
* Links to CSS files
* Links to YUI libraries (this class knows about the dependancies between the different libs).
* Skip links that go from the top of <body> to various places in the content.
* Calls to JavaScript functions (for example to initialise things)
* Bits of data from PHP that need to be available to JavaScript
* As a special case of that, an easy way to pass language strings to JS.