SDL/SDL2 fullscreen mouse fixes
- SDL/SDL2: fixed mouse movement in absolute x/y mode
- SDL2: always capture mouse in fullscreen mode (like legacy SDL gui)
- SDL: don't handle headerbar click in fullscreen mode
- SDL/SDL2 code sync


git-svn-id: svn://svn.code.sf.net/p/bochs/code/trunk@12394 6c8e4198-a580-4521-a02f-c9ae86df1db9