Flash: added LoaderContext.checkPolicyFile to ImageLoader request

Adds a simple LoaderContext to the loader.load in ImageLoader (flash target only).

This is required because ImageLoader accesses the bitmapData directly, which throws a Security Sandbox exception when loading from another domain with a valid crossdomain.xml

	override function loaderLoad()
	{
		...
		var loaderContext = new flash.system.LoaderContext(true);
		loader.load(new flash.net.URLRequest(url), loaderContext);
		...
	}