Merge branch 'cc/skip' into HEAD

* cc/skip:
  Bisect: add "skip" to the short usage string.
  Bisect run: "skip" current commit if script exit code is 125.
  Bisect: add a "bisect replay" test case.
  Bisect: add "bisect skip" to the documentation.
  Bisect: refactor "bisect_{bad,good,skip}" into "bisect_state".
  Bisect: refactor some logging into "bisect_write".
  Bisect: refactor "bisect_write_*" functions.
  Bisect: implement "bisect skip" to mark untestable revisions.
  Bisect: fix some white spaces and empty lines breakages.
  rev-list documentation: add "--bisect-all".
  rev-list: implement --bisect-all