Double Hi-Res B&W output is shifted

[fadden]

The B&W conversion mode for double-hi-res graphics is shifted 4 pixels to the right. The problem is that this:

            if (!pixelBits[idx]) {
                colorBuf[bufTarget] = kColorBlack;
            } else {
                colorBuf[bufTarget] = kColorWhite;
            }

fails to take into account the look-behind buffer. It should be:

            if (!pixelBits[idx + kMaxLook]) {