INT 31 - VIRUS - "Vacsina" series - INSTALLATION CHECK (NOT A VECTOR!)

Note:	if one of the Vacsina viruses is resident, the low byte of this
	  interrupt still contains the last byte of the INT 30 CP/M JMP
	  instruction, but the remaining three bytes are 7Fh 39h followed
	  by the Vacsina version number
SeeAlso: INT 21/AX=FFFFh"VIRUS",INT 32"VIRUS"