I'm not a fan of this part of MonoGame...  the work around the content pipeline and XNBs part...  but if we have it here for now it needs to work.  

My concern here is I think this change will throw exceptions.  If you look at `ReadRawAsset`....

https://github.com/mono/MonoGame/blob/develop/MonoGame.Framework/Content/ContentManager.cs#L387

... you see at least in the case of effects and textures it calls `TitleContainer.OpenStream` which internally requires a relative path.  I suspect the other types internally all use the same method to open files causing the same error.