fixup_bundle.unix: support a "plugin" module type
The difference between "plugin" and "module" is that plugins install novel dependencies into the library where they live. The logic path for this isn't the nicest right now.
This addresses paraview-superbuild#159 (closed) by installing plugin-specific libraries beside the plugin itself (as they should be).
@aron.helser @dcthomp Note that this may affect cmb-superbuild negatively until paraview!4602 (merged) lands (though it will be "just" a ParaView upgrade if we set the default to ON
).