When testing existing sketches I needed to remove references to 'screen'.

I wasn't sure if this was an official Processing API member or just a
leftover convenience variable, but I see it listed here:
http://processing.org/reference/screen.html so I'm reporting it as a bug :)

yeah, it's screenW and screenH for android (in 0178.. it's not in the
current release). we shouldn't have documented it in the reference on the
desktop version, and i'll be added screenW/H to the desktop release and
marking 'screen' as deprecated. i wouldn't otherwise, but the
java.awt.Dimension class isn't available in android, and using an object
like that isn't in line w/ the rest of the api even for the desktop version.

oops, that's screenWidth and screenHeight. tho maybe screenW/H is better
since it's more like mouseX/Y.

in fact, i'm going with screenW and screenH, and unlike 'screen', they'll
also be static like they should be. so i've added them to both releases of
core for 0178.