Add some more graphics feature and limit queries (resolves issue #1234).

love.graphics.getSupported():
 - Added “fullnpot” field, is true everywhere except on some older mobile devices. If false, mipmapping and wrap modes other than “clamp” can’t be used on non-power-of-two sized textures.
 - Added “pixelshaderhighp” field, is true everywhere except some older mobile devices. If false, “highp” precision can’t be used in pixel shaders and love will default to “mediump” instead.

love.graphics.getSystemLimits():
- Added “anisotropy” field, gets the maximum amount of anisotropy you can specify in Texture:setFilter. love will clamp anisotropy arguments greater than this value.

--HG--
branch : minor

src/modules/graphics/Graphics.h

@@ -151,6 +151,8 @@ public:
 		FEATURE_MULTI_CANVAS_FORMATS,
 		FEATURE_CLAMP_ZERO,
 		FEATURE_LIGHTEN,
+		FEATURE_FULL_NPOT,
+		FEATURE_PIXEL_SHADER_HIGHP,
 		FEATURE_MAX_ENUM
 	};
 
@@ -167,6 +169,7 @@ public:
 		LIMIT_TEXTURE_SIZE,
 		LIMIT_MULTI_CANVAS,
 		LIMIT_CANVAS_MSAA,
+		LIMIT_ANISOTROPY,
 		LIMIT_MAX_ENUM
 	};