TODO:
* Are there instances where we might want to restrict CSS as well as JS?
* Would a $wg config option and/or user preference and/or index.php GET parameter to limit inclusion be useful?
* Can we deprecate any of the existing $wg config options?
* What's going on with the duplicated code between OutputPage and SkinTemplate?
* Interpreted some Trevor-speak in the doc comment of ResourceLoader::preloadModuleInfo().
* Made setMsgBlobMtime() (called from preloadModuleInfo()) actually work, by making getMsgBlobMtime() use the cached blob times if they are available.
* Break long lines.
* Convert long or unnecessary ternary operator usages to if/else.
* Fixed excessively clever assignment expressions.
* Rename $cache to $cacheEntry.
* Removed unnecessary web invocation guards. Their perlish form was making me uncomfortable. BTW, unlike in Perl, die() is not a function, it's a special case in the PHP grammar which very roughly simulates the Perl syntax:
die "x"; // works
0 || die("x"); // works
0 || (die); // works
0 || (die "x"); // fail!
