Output from "git diff" can be made easier to read by selecting
which lines are common and which lines are added/deleted
intelligently when the lines before and after the changed section
are the same.  A command line option is added to help with the
experiment to find a good heuristics.

* mh/diff-indent-heuristic:
  blame: honor the diff heuristic options and config
  parse-options: add parse_opt_unknown_cb()
  diff: improve positioning of add/delete blocks in diffs
  xdl_change_compact(): introduce the concept of a change group
  recs_match(): take two xrecord_t pointers as arguments
  is_blank_line(): take a single xrecord_t as argument
  xdl_change_compact(): only use heuristic if group can't be matched
  xdl_change_compact(): fix compaction heuristic to adjust ixo