Merge branch 'pw/add-p-hunk-splitting-fix'

Marking a hunk 'selected' in "git add -p" and then splitting made all the split pieces 'selected'; this has been changed to make them all 'undecided', which gives better end-user experience. * pw/add-p-hunk-splitting-fix: add-patch: update hunk splitability after editing add -p: mark split hunks as undecided