Merge branch 'jc/blame'

* jc/blame:
  blame -S <ancestry-file>
  Match ofs/cnt types in diff interface.
  blame: use built-in xdiff
  combine-diff: move the code to parse hunk-header into common library.
  combine-diff: refactor built-in xdiff interface.
  combine-diff: use built-in xdiff.

diff --cc Makefile
Simple merge

diff --cc blame.c
Simple merge