Ensured compatibility with MonoGame for iOS.

iOS MonoGame has no implementation for GetData/SetData, however we don't need to worry about the volatility of Textures with regards to screen resolution re-size as this is not an issue on iOS.

spine-xna/src/Util.cs

@@ -76,6 +76,9 @@ namespace Spine {
 			// Release the GPU back to drawing to the screen
 			device.SetRenderTarget(null);
 
+#if IOS
+			return result as Texture2D;
+#else
 			// RenderTarget2D are volatile and will be lost on screen resolution changes.
 			// So instead of using this directly, we create a non-voliate Texture2D.
 			// This is computationally slower, but should be safe as long as it is done
@@ -89,6 +92,7 @@ namespace Spine {
             result.Dispose();
       			
 			return resultTexture;
+#endif
 		}
 	}
 }