Added a NativePreviewEvent to replce the current EventPreview system.  Now, multiple widgets can preview the same event, instead of just the one at the top of the stack.  This fixes a couple of subtle bugs and adds some use cases, such as listening for user timeout.

Patch by: jlabanca
Review by: ecc
Issue: 1275



git-svn-id: https://google-web-toolkit.googlecode.com/svn/releases/1.6@4385 8db76d5a-ed1c-0410-87a9-c151d255dfc7
16 files changed