Merge branch 'lm/add-p-context'

"git add/etc -p" now honor the diff.context configuration variable, and also they learn to honor the -U<n> command-line option. * lm/add-p-context: add-patch: add diff.context command line overrides add-patch: respect diff.context configuration t: use test_config in t4055 t: use test_grep in t3701 and t4055