INT 13 - QUICKCACHE II v4.20 - FLUSH CACHE

	AH = 21h
Return: AX = status (0000h successful)
Desc:	immediately write all dirty sectors back to disk
Note:	this is one out of several cache flush calls issued by the PTS-DOS 6.51
	  and S/DOS 1.0 kernel before rebooting. It is called with DL=80h and
	  conflicts with the PS/2 function of the same function number, because
	  the kernel does not perform Quickcache's installation check first.
SeeAlso: AH=25h"QUICKCACHE",AH=2Eh,AH=2Fh