For consistency, the `load` call should always be asynchronous, event
when the resource is readily available in cache.

Add unit tests (unittests_three.html only).
Update QUnit to latest version.

Fixes #6779. Does NOT fix #6572.

Not too happy about it, but at least it's starting to be consistent. It's more of a monitor though...

It happens on a project I'm working on, not sure still why. I guess this approach is safer.

This fixes broken custom blending example.

That took a while... but I think it makes sense...

Tried to make it as straight foward as possible. Kept the extrac base url thingie :)
Thinking of moving BinaryLoader to examples/js/loaders.... what do you think @alteredq?

Using xhr.addEventListener instead of xhr.onreadystatechange. Changed 'complete' event to 'load' as native JavaScript.

The only confusing part of this approach is the event object that gets dispatched. For ImageLoader you need to look for event.image, and for OBJLoader you need to look for event.object. Maybe it should be consistent for all and just be event.content?

Hesitant on whether this should extend Loader or not. I guess we'll see whether is needed or not once we have more features.

Tinkering with the problem of images loading async...
Maybe this should be TextureLoader instead...