Merge branch 'bp/commit-p-editor'

When it is not necessary to edit a commit log message (e.g. "git commit -m" is given a message without specifying "-e"), we used to disable the spawning of the editor by overriding GIT_EDITOR, but this means all the uses of the editor, other than to edit the commit log message, are also affected. * bp/commit-p-editor: run-command: mark run_hook_with_custom_index as deprecated merge hook tests: fix and update tests merge: fix GIT_EDITOR override for commit hook commit: fix patch hunk editing with "commit -p -m" test patch hunk editing with "commit -p -m" merge hook tests: use 'test_must_fail' instead of '!' merge hook tests: fix missing '&&' in test