Added some workarounds for the win32 fullscreen mode
- changing from window mode to fullscreen and back now looks okay
- changing guest resolution in fullscreen mode now also works
- TODO #1: rewrite of the window / fullscreen code to avoid using dimension_update()
  to toggle the internal mode
- TODO #2: add size checks in dimension_update() to avoid crash. We could panic
  at this point or compress screen to desktop size.


git-svn-id: svn://svn.code.sf.net/p/bochs/code/trunk@12333 6c8e4198-a580-4521-a02f-c9ae86df1db9