Continued work on win32 fullscreen rewrite
- fixed screen flickering after entering fullscreen for the second time
- now using resize_main_window() directly for leaving fullscreen mode
- dimension_update() now only used for guest display mode change
- TODO: more testing to find cases that can make Bochs crash


git-svn-id: svn://svn.code.sf.net/p/bochs/code/trunk@12335 6c8e4198-a580-4521-a02f-c9ae86df1db9