Add SDL_GL_ResetAttributes.

--HG--
extra : rebase_source : 0a6fd1c977ab93ba651adaae3fa5a71d7c69fa8e

include/SDL_video.h

@@ -865,6 +865,11 @@ extern DECLSPEC void SDLCALL SDL_GL_UnloadLibrary(void);
 extern DECLSPEC SDL_bool SDLCALL SDL_GL_ExtensionSupported(const char
                                                            *extension);
 
+/**
+ *  \brief Reset all previously set OpenGL context attributes to their default values
+ */
+extern DECLSPEC void SDLCALL SDL_GL_ResetAttributes(void);
+
 /**
  *  \brief Set an OpenGL window attribute before window creation.
  */