Log Message:
backuppc: update to 4.4.0

This release contains several new features and some bug fixes.
New features include:
- any full/filled backup can be marked for keeping, which prevents any
  expiry or deletion
- any backup can be annotated with a comment (eg, "prior to upgrade of \ 
xyz")
- added metrics CGI that replaces RSS and adds Prometheus support
- tar XferMethod now supports xattrs and acls
- rsync XferMethod now correctly supports xattrs on directories and symlinks
- nightly pool scanning now verifies the md5 digests of a configurable
  fraction of pool files
- code runs through perltidy so format is now uniform