sysutils/bup: Update to 0.29.3

Upstream changes (other than bugfixes minor improvements):

0.29.3:

* Newer versions of par2 can process in parallel using multiple
  threads/cores, and they do so automatically.  This ends up competing
  with `bup fsck`s own parallelism, enabled by `-j`, in such a way
  that the command can actually run much *slower* (and be much more
  expensive) than it would have been with no parallelism at all.

  When appropriate `bup fsck` now disables par2's competing
  parallelism (via its `-t1` option) to avoid the contention.

0.29.0:

* An experimental `prune-older` command has been added.  It removes
  (permanently deletes) all saves except those preserved by a set of
  arguments like `--keep-monthlies-for 3y`.  See `bup help
  prune-older` for further information.

(gdt)