Merge branch 'jk/diff-compact-heuristic'

Patch output from "git diff" and friends has been tweaked to be more readable by using a blank line as a strong hint that the contents before and after it belong to a logically separate unit. * jk/diff-compact-heuristic: diff: undocument the compaction heuristic knobs for experimentation xdiff: implement empty line chunk heuristic xdiff: add recs_match helper function