Increase IOHelper.copyStream buffer size to 8KB
Increase IOHelper.copyStream buffer size to 8KB

This matches the default buffer size used by BufferedInput/OutputStream.

Code Review:  http://codereview.appspot.com/194910043/

dweidenfeld/library,dweidenfeld/library,googlegsa/library,dweidenfeld/library,googlegsa/library,googlegsa/library