INT 21 - FlashTek X-32VM - ALLOCATE PROTECTED-MODE SELECTOR

	AX = 3501h
Return: CF clear if successful
	    BX = new selector
	CF set on error (no more selectors available)
Note:	the new selector will be an expand-up read/write data selector with
	  undefined base and limit
SeeAlso: AX=3502h,INT 31/AX=0000h