Update py-barman to 1.4.0.

Version 1.4.0 - 26 Jan 2015

  * Incremental base backup implementation through the reuse_backup
    global/server option. Possible values are off (disabled,
    default), copy (preventing unmodified files from being
    transferred) and link (allowing for deduplication through hard
    links).
  * Store and show deduplication effects when using reuse_backup=
    link.
  * Added transparent support of pg_stat_archiver (PostgreSQL 9.4) in
    check, show-server and status commands.
  * Improved administration by invoking WAL maintenance at the end of
    a successful backup.
  * Changed the way unused WAL files are trashed, by differentiating
    between concurrent and exclusive backup cases.
  * Improved performance of WAL statistics calculation.
  * Treat a missing pg_ident.conf as a WARNING rather than an error.
  * Refactored output layer by removing remaining yield calls.
  * Check that rsync is in the system path.
  * Include history files in WAL management.
  * Improved robustness through more unit tests.
  * Fixed bug #55: Ignore fsync EINVAL errors on directories.
  * Fixed bug #58: retention policies delete.

(fhajny)