INT 16 - PC Tools v5.1+ DESKTOP API - ALTERNATE INSTALLATION CHECK
AX = FFF1h
BX = 0000h  leave ??? flag as is
nonzero set ??? flag
Return: CX = 5555h if installed
DX = 5555h


16FFF1BX0000 - PC Tools v5.1+ DESKTOP API - ALTERNATE INSTALLATION CHECK