Some more work on the win32 fullscreen mode
- moved fullscreen mode enable/disable stuff to a new function
- now only use dimension_update() for leaving fullscreen mode
- fixed fullscreen issues in text mode
- TODO: check if guest display is too large and add a proper handling for this case


git-svn-id: svn://svn.code.sf.net/p/bochs/code/trunk@12334 6c8e4198-a580-4521-a02f-c9ae86df1db9