Merge branch 'jc/checkdiff'

* jc/checkdiff: Fix t4017-diff-retval for white-space from wc Update sample pre-commit hook to use "diff --check" diff --check: detect leftover conflict markers Teach "diff --check" about new blank lines at end checkdiff: pass diff_options to the callback check_and_emit_line(): rename and refactor diff --check: explain why we do not care whether old side is binary