Fix the computation of the window size.

When the requested window size did not fit in the screen, the ratio applied to
the size must be applied to the requested size, not the screen size.

Also, the double/int mix used to create a 0x0 window.
Fix .desktop files syntax errors.

The MimeType entry must end with a semicolon. Thanks Dmitriy Perlow.
Make running-bear optional.

running-bear is not needed anymore, so it is now disabled by default.
Define RUNNING_BEAR_ENABLED=true to compile it.
Merge branch 'master' of github.com:j-jorge/bear into android-port
[SDL2] Update screen management with SDL 2's API.

SDL_SetVideoMode() does not exist anymore. We use SDL_CreateWindow() instead,
followed by SDL_GL_CreateContext.

We keep the pointer returned by this CreateWindow to get the size of the window
in the places where SDL_GetVideoInfo() and SDL_GetVideoSurface where used.

m_display_size is not needed anymore. We use SDL_GetDesktopDisplayMode() to find
the initial screen resolution.

Finding the most suitable screen resolution is done with SDL_GetDisplayMode().

The event processing uses the new SDL_PeepEvents() interface and searches only
for SDL_QUIT. I am not sure that the old loop was not incorrect.