INT 31 P - CauseWay - "GetSel" - ALLOCATE NEW SELECTOR
AX = FF03h
Return: CF clear if successful
BX = new selector
CF set on error
Note: the new selector is initialized with a base address of 000000h, a limit
of 0000h, and attributes read/write expand-up data
SeeAlso: AX=FF04h,AX=FF05h,AX=FF06h