More backup improvements:
- Changed get_backup_name() to verify the backup path, and make any
missing directories. This avoids accidental use of a symlink as a dir
in a backup path, and gets rid of any other non-dirs that are in the
way. It also avoids the need for various operations to retry after
calling make_bak_dir(), simplifying several pices of code.
- Changed create_directory_path() to make_path(), giving it flags that
lets the caller decide if it should skip a leading slash or drop the
trailing filename.
- Mention when we create the backup directory, so the user is not caught
unaware when rsync uses a directory they didn't expect.
- Got rid of some dir-moving backup code that is not used.
- Added a little more backup-debug output.