- `mariadb-backup --backup` was fixed to fetch the value of the
   @@aria_log_dir_path server variable and copy aria_log* files
   from @@aria_log_dir_path directory to the backup directory.
   Absolute and relative (to --datadir) paths are supported.

   Before this change aria_log* files were copied to the backup
   only if they were in the default location in @@datadir.

- `mariadb-backup --copy-back` now understands a new my.cnf and command line
   parameter --aria-log-dir-path.

  `mariadb-backup --copy-back` in the main loop in copy_back()
   (when copying back from the backup directory to --datadir)
   was fixed to ignore all aria_log* files.

   A new function copy_back_aria_logs() was added.
   It consists of a separate loop copying back aria_log* files from
   the backup directory to the directory specified in --aria-log-dir-path.
   Absolute and relative (to --datadir) paths are supported.
   If --aria-log-dir-path is not specified,
   aria_log* files are copied to --datadir by default.

- The function is_absolute_path() was fixed to understand MTR style
  paths on Windows with forward slashes, e.g.
   --aria-log-dir-path=D:/Buildbot/amd64-windows/build/mysql-test/var/...