Make cursor visible when disabling mousegrab

ChangeLog

 	[ 20140312 ]
 	* Resizing the window works properly (except for fixed string positions)
 	* Removed FullScreen config command and flag that had no effect
+	* Set cursor visible when disabling mousegrab
 
 	[ 20140311 ]
 	* Removed empty Camera, Matrix, Particle, Quaternion,

src/SDLSystem.cpp

 
 void SDLSystem::setGrabMouse(bool on) {
     SDL_SetRelativeMouseMode(on ? SDL_TRUE : SDL_FALSE);
+    if (!on)
+        SDL_ShowCursor(1);
 }
 
 void SDLSystem::initVideo(unsigned int width, unsigned int height, bool fullscreen) {