Use real double buffering instead.
I checked the SDL code and if the hardware cannot provide double buffering
it will use a shadow surface to ensure that a frame is not displayed until
it has been fully painted.
Also disable mouse cursor before opening the output surface. The reason it
was disabled after the surface was opened is that SDL on GP2X has a bug.
However, this means the cursor is visible for a short time during startup
which looks ugly.
Removed all methods that are never called.
Made methods that are only called by Surface itself private.
One ugly thing remaining is outside access to the "raw" field.
