Merge branch 'cc/bisect' (early part)

* 'cc/bisect' (early part):
  t6030: test skipping away from an already skipped commit
  bisect: when skipping, choose a commit away from a skipped commit
  bisect: add parameters to "filter_skipped"
  bisect: display first bad commit without forking a new process
  bisect: drop unparse_commit() and use clear_commit_marks()