Merge branch 'by/diff-graph'

* by/diff-graph:
  Make --color-words work well with --graph
  graph.c: register a callback for graph output
  Emit a whole line in one go
  diff.c: Output the text graph padding before each diff line
  Output the graph columns at the end of the commit message
  Add a prefix output callback to diff output

Conflicts:
	diff.c