Expand support for different screen sizes.

Expand support for different screen sizes.

Applications can now declare that they support small, normal, or
large screens.  Resource selection can also be done based on these
sizes.  By default, pre-Donut apps are false for small and large,
and Donut or later apps are assumed to support all sizes.  In either
case they can use <supports-screens> in their manifest to declare
what they actually support.