support -m"<msg>" combined with commit --fixup

Here's a hopefully ready to apply v2 incorporating feedback from Eric (thanks!). A tbdiff with v1 follows below.

Ævar Arnfjörð Bjarmason (2):
commit doc: document that -c, -C, -F and --fixup with -m error
commit: add support for --fixup <commit> -m"<extra message>"

 Documentation/git-commit.txt | 2 ++
 builtin/commit.c             | 8 +++++---
 t/t7500-commit.sh            | 9 ++++++++-
 3 files changed, 15 insertions(+), 4 deletions(-)

1: 7d5e2531ee ! 1: 82333992ec commit doc: document that -c, -C, -F and --fixup with -m error

    @@ -7,6 +7,7 @@
         explicitly since 0c091296c0 ("git-commit: log parameter updates.",
         2005-08-08), but the documentation was never updated to reflect this.
         
    +    Wording-by: Eric Sunshine <[email protected]>
         Signed-off-by: Ævar Arnfjörð Bjarmason <[email protected]>
     
     diff --git a/Documentation/git-commit.txt b/Documentation/git-commit.txt
    @@ -17,8 +18,8 @@
      	If multiple `-m` options are given, their values are
      	concatenated as separate paragraphs.
     ++
    -+Combining the `-m` option and any of `-c`, `-C`, `-F` or `--fixup`
    -+will result in an error.
    ++The `-m` option is mutually exclusive with `-c`, `-C`, `-F`, and
    ++`--fixup`.
      
      -t <file>::
      --template=<file>::

2: bd78a211ed ! 2: 780de6e042 commit: add support for --fixup <commit> -m"<extra message>"
@@ -22,6 +22,21 @@
In such a case you might want to leave a small message,
e.g. "forgot this part, which broke XYZ".

+ With this, --fixup <commit> -m"More" -m"Details" will result in a
+ commit message like:
+
+ !fixup <subject of <commit>>
+
+ More
+
+ Details
+
+ The reason the test being added here seems to squash "More" at the end
+ of the subject line of the commit being fixed up is because the test
+ code is using "%s%b" so the body immediately follows the subject, it's
+ not a bug in this code, and other tests t7500-commit.sh do the same
+ thing.
+
When the --fixup option was initially added the "Option -m cannot be combined" error was expanded from -c, -C and -F to also include --fixup[1]
@@ -34,6 +49,7 @@
1. d71b8ba7c9 ("commit: --fixup option for use with rebase --autosquash", 2010-11-02)

+ Helped-by: Eric Sunshine <[email protected]>

diff --git a/Documentation/git-commit.txt b/Documentation/git-commit.txt
@@ -43,10 +59,9 @@
If multiple -m options are given, their values are concatenated as separate paragraphs.
+
--Combining the -m option and any of -c, -C, -F or --fixup --will result in an error.
-+Combining the -m option and any of -c, -C or -F will result in -+an error.
+-The -m option is mutually exclusive with -c, -C, -F, and +---fixup.
++The -m option is mutually exclusive with -c, -C, and -F.

-t <file>::
--template=<file>::

2.15.1.424.g9478a66081