Merge branch 'da/difftool-mergetool-simplify-reporting-status'

Code simplification. * da/difftool-mergetool-simplify-reporting-status: mergetools: stop setting $status in merge_cmd() mergetool: simplify conditionals difftool--helper: add explicit exit statement mergetool--lib: remove use of $status global mergetool--lib: remove no-op assignment to $status from setup_user_tool