Release all pressed keys when the simulation window gets back the keyboard
focus. This change will fix some keyboard-related bug reports (DONE for the
x and sdl2 guis / TODO for all others).


git-svn-id: svn://svn.code.sf.net/p/bochs/code/trunk@12581 6c8e4198-a580-4521-a02f-c9ae86df1db9