MGASA-2018-0454 Updated sdl2/mingw-SDL2 packages fix security vulnerabilities

This update fixes various security vulnerabilities affecting the SDL2image library, listed below. The fixes are provided in SDL2image 2.0.4, which depends on SDL2 2.0.8 or later. As such, the SDL2 and SDL2mixer libraries are also updated to their current stable releases, providing various bug fix...