#203 SDL UI, strange behaviour when WM aborts fullscreen

[Sergio Baldoví]

Running at fullscreen with the SDL user interface, the window manager could change the state of the main window to windowed, e.g, a popup of jdownloader could request user's attention.

Actual result:
1. window state change to windowed
2. mouse pointer is invisible
3. settings_current.full_screen and sdldisplay_is_full_screen are out of sync
4. after interacting with the menu some kind of refresh goes back to fullscreen

Expected result:
1. window state change to windowed
2. mouse pointer becomes visible
3. settings_current.full_screen and sdldisplay_is_full_screen set to false
4. windowed state remains until user's choice

[Fredrick Meunier]

Patch welcome :)