Fix issue #74

See the comment in the code for an explanation of the fix.
The problem in issue #74 is due to the fact that "Assembly.LoadFile" loads assembly in "no context" and so Fusion can't find the dependencies of such an assembly and fires another AssemblyResolve event. If such dependencies aren't already loaded or embedded in the executable, Costura's handler can't find them and we'll get an FileLoad exception. That exception can simply be fixed by giving Fusion a try to load such dependencies with Assembly.Load.