Merge branch 'jk/diff-graph-cleanup'

Refactors a lot of repetitive code sequence from the graph drawing code and adds it to the combined diff output. * jk/diff-graph-cleanup: combine-diff.c: teach combined diffs about line prefix diff.c: use diff_line_prefix() where applicable diff: add diff_line_prefix function diff.c: make constant string arguments const diff: write prefix to the correct file graph: output padding for merge subsequent parents