There is a new implementation of require_js in lib/deprecatedlib.php,
based on $PAGE->requires.

There were a few other recently introduced functions in lib/weblib.php,
namely print_js_call, print_delayed_js_call, print_js_config and
standard_js_config. These have been removed, since they were never in
a stable branch, and all the places that used them have been changed
to use the newer $PAGE->requires->... methods.

get_require_js_code is also gone, and the evil places that were calling
it, even though it is an internal function, have been fixed.

Also, I made some minor improvements to the code I committed yesterday
for MDL-16695.

All that remains is to update all the places in core code that are
still using require_js.

(This commit also fixes the problem where the admin tree would not
start with the right categories expanded.)