from 2.5.6 to 2.5.7
- fixed bug leading dar to not include directories given to -g option nor
  to exclude directories given to -P option when at the same time the
  directory given to -R option starts by a dot ("-R ./here" in place of
  "-R here")
- bug fix and speed improvement: under certain circumstances dar was
  reading several times the data at slice boundary, leading dar to ask for
  slice N then N-1 then again N, this caused sub-optimal performance and
  was triggering user script unnecessarily