INT 13 - QUICKCACHE II v4.20 - SET BUFFERED READ

	AH = 2Dh
	AL = new state (00h disabled, 01h enabled)
Return: AX = status (0000h successful)
Desc:	specify whether the cache should attempt to read ahead of actual
	  requests
Note:	this function enables or disables read-ahead for all drives; use AH=37h
	  to change a single drive
SeeAlso: AH=2Ch,AH=37h