Fix a race wherein the source of an interrupt vector is wrongly
attributed if an ExtINT arrives during interrupt injection.

Also, fix a spurious interrupt if the PIC tries to raise an interrupt
before the outstanding one is accepted.

Finally, improve the PIC interrupt latency when another interrupt is
raised immediately after the outstanding one is accepted by creating a
vmexit rather than waiting for one to occur by happenstance.

Approved by:	neel (co-mentor)