Merge branch 'ab/commit-m-with-fixup'

"git commit --fixup" did not allow "-m<message>" option to be used at the same time; allow it to annotate resulting commit with more text. * ab/commit-m-with-fixup: commit: add support for --fixup <commit> -m"<extra message>" commit doc: document that -c, -C, -F and --fixup with -m error