Make exclusion work in a more obvious manner.
Make exclusion work in a more obvious manner.

By comparing against installdir instead of staging_path we can write
exclusions as working against the top level of the source directory,
without requiring reproducing the prefix.

Also log the actual matched path rather than the full path, for
clarity.

djhaskin987/fpm,djhaskin987/fpm,djhaskin987/fpm,djhaskin987/fpm