MUL/IMUL flag setting is incorrect

[neldredge]

mul bl currently sets the carry and overflow flags if ah was nonzero on input. It should set them if ah is nonzero on output. I think somebody misread the manual.

The same goes for the other multiply instructions. Additionally, the flag set logic in IMUL is incorrect. It clears/sets them according to whether AH is equal to 0xff. Instead they should be cleared if AH equals the sign bit of AL (0xff or 0x00 as appropriate), otherwise set.