Add handlers for delay and sleep callbacks.
Fix sceKernelReferThreadRunStatus() layout.

Was missing size, so all fields were wrong.
Don't allow sceKernelWakeupThread() on cur thread.

I don't know why you wouldn't allow this, but the PSP firmware doesn't.
Add handlers for callbacks during mbx waits.
Implement VPL/FPL callback handlers.

Smells like time to refactor, there are less differences than I expected.
Refactor down the begin/end callback stuff.
Handle it better when umd waits trigger during cbs.
Merge pull request #3583 from unknownbrackets/callbacks

Callback and minor scheduling fixes