Add a new “stencil8” pixel format for Canvases (resolves issue #1003).

Also fixed Canvas MSAA (resolves issue #1271).

stencil-formatted Canvases can’t be drawn, and can only be used as the value for a new ‘depthstencil’ field to the table-argument variant of love.graphics.setCanvas.

--HG--
branch : minor

src/modules/graphics/Shader.h

@@ -190,6 +190,7 @@ public:
 
 	TextureType getMainTextureType() const;
 	void checkMainTextureType(TextureType textype) const;
+	void checkMainTexture(Texture *texture) const;
 
 	virtual ptrdiff_t getHandle() const = 0;