Improve delete to show about reasons why backup cannot be deleted.
Improve delete to show about reasons why backup cannot be deleted.

In delete command, pg_rman delete only before the latest and validated
full backup until the specified DATE. However, pg_rman does not show
anything about this behavior, and this makes users confused.

bwtakacy/prev_pg_rman_repo,bwtakacy/prev_pg_rman_repo