INT 62 u - FGDRIVER v4.02 - "FG_XALPHA" - CONVERT SCREEN COLUMN TO CHAR COLUMN
	AX = 00E1h
	BX = screen space column
Return: AX = character space column containing specified coordinate
Note:	the FGDRIVER functions are rearranged with each major release, but
	  their parameters do not change (see #03474 at AX=0000h)
SeeAlso: AX=00E2h,AX=00E4h