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.
Set default flag attributes

The flag options defined as "--[no-]foo" were being set in the
attributes hash as :"[no_]foo" => true/false.

This change may break other tests, as it sets up the defaults in the
test cases according to the option definition, rather than defaulting to
false (as previously).
Merge pull request #494 from agenticarus/feature/exclude-paths

Make exclusion work in a more obvious manner.
Merge pull request #496 from dsludwig/master

Set default flag attributes