Update to 0.56.3

  pkg_src_summary:
    - fixed: gathering DESCRIPTION and ALLDISTFILES fields eats
      too much CPU. Now full summary is gathered drammatically faster.
      This may significantly speed up distbb bulk builds.
    - While generating ALLDISTFILES do not try to read "distinfo" files when
      DISTFILES is empty.
    - More regression tests.
    - If MAKECONF and PSS_SLAVES are not empty, MAKECONF is passed to
      pkg_src_summary processes running on slave hosts.

(cheusov)