Minor changes for cameras.xml

Hey, 

You changed the 20D to CFA2 for testing, but there are enough CFA2 entries now, that the Canon can go back to regular CFA, so that's more or less consistent again.

Also, the whitepoint for the D800 is different from what Adobe DNG Converter reports. Was this different for a reason? And didn't Nikon include curves in their NEFs about how to handle the white level? So presumably the white level parameter is ignored anyhow?