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/Texture.h

@@ -120,6 +120,8 @@ public:
 	TextureType getTextureType() const;
 	PixelFormat getPixelFormat() const;
 
+	bool isReadable() const;
+
 	int getWidth() const;
 	int getHeight() const;
 	int getDepth() const;
@@ -166,6 +168,7 @@ protected:
 	TextureType texType;
 
 	PixelFormat format;
+	bool readable;
 
 	int width;
 	int height;