Rework the code that copies assemblies and their related files to the app
bundle to take into account that we might be building to frameworks now.
Also strip the assemblies when they're copied (if they must be stripped),
which removes the need for custom logic to copy files related to stripped
assemblies.
Additionally change how we handle duplicated assemblies by checking for
duplication before copying them to the app bundle. This allows us to copy
assemblies to the root directory (not the .monotouch-[32|64] subdirectory) if
the 32-bit and 64-bit versions are identical, which also means we won't need
symlinks anymore.