INT 13 - QUICKCACHE II v4.20 - SET FLUSH INTERVAL

	AH = 25h
	BX = interval
Return: AX = status (0000h successful)
Desc:	specify how often the cache should write dirty buffers to disk when
	  buffered writes are enabled
SeeAlso: AH=21h"QUICKCACHE",AH=2Ch,AH=2Eh