AWT buffer strategies

I finished GNU Classpath’s BufferStrategy framework tonight:

AWT BufferStrategy test.

Currently there is only one unaccelerated backend that doesn’t actually do anything, but the framework for adding new backends is in place as well as all the necessary documentation.

This patch adds the missing methods that Caolan mentioned in his blog. This is the last GCJ AWT vs. problem I’m aware of, so I think we’re in good shape for Fedora Core 4.