Merge branch 'mm/diff-U-takes-no-negative-values'

The command line parser for "git diff" learned a few options take only non-negative integers. * mm/diff-U-takes-no-negative-values: parse-options: clarify what "negated" means for PARSE_OPT_NONEG xdiff: guard against negative context lengths diff: reject negative values for -U/--unified diff: reject negative values for --inter-hunk-context