Add the ability to have formally deprecated functions.

Functions which are deprecated will print out a message and show up in a small dialog on-screen, when they're first called. Deprecation output is disabled in fused mode by default, and can be modified with love.setDeprecationOutput(enable).

--HG--
branch : minor

src/modules/graphics/opengl/Graphics.cpp

@@ -899,6 +899,8 @@ void Graphics::present(void *screenshotCallbackData)
 	if (isCanvasActive())
 		throw love::Exception("present cannot be called while a Canvas is active.");
 
+	deprecations.draw(this);
+
 	flushStreamDraws();
 	endPass();