C style: use standard style for "TRANSLATORS" comments

C style: use standard style for "TRANSLATORS" comments

Change all the "TRANSLATORS: [...]" comments in the C code to use the
regular Git coding style, and amend the style guide so that the
example there uses that style.

This custom style was necessary back in 2010 when the gettext support
was initially added, and was subsequently documented in commit
cbcfd4e3ea ("i18n: mention "TRANSLATORS:" marker in
Documentation/CodingGuidelines", 2014-04-18).

GNU xgettext hasn't had the parsing limitation that necessitated this
exception for almost 3 years. Since its 0.19 release on 2014-06-02
it's been able to recognize TRANSLATOR comments in the standard Git
comment syntax[1].

Usually we'd like to keep compatibility with software that's that
young, but in this case literally the only person who needs to be
using a gettext newer than 3 years old is Jiang Xin (the only person
who runs & commits "make pot" results), so I think in this case we can
make an exception.

This xgettext parsing feature was added after a thread on the Git
mailing list[2] which continued on the bug-gettext[3] list, but we
never subsequently changed our style & styleguide, do so.

There are already longstanding changes in git that use the standard
comment style & have their TRANSLATORS comments extracted properly
without getting the literal "*"'s mixed up in the text, as would
happen before xgettext 0.19.

Commit 7ff2683253 ("builtin-am: implement -i/--interactive",
2015-08-04) added one such comment, which in commit df0617bfa7 ("l10n:
git.pot: v2.6.0 round 1 (123 new, 41 removed)", 2015-09-05) got picked
up in the po/git.pot file with the right format, showing that Jiang
already runs a modern xgettext.

The xgettext parser does not handle the sort of non-standard comment
style that I'm amending here in sequencer.c, but that isn't standard
Git comment syntax anyway. With this change to sequencer.c & "make
pot" the comment in the pot file is now correct:

     #. TRANSLATORS: %s will be "revert", "cherry-pick" or
    -#. * "rebase -i".
    +#. "rebase -i".

1. http://git.savannah.gnu.org/cgit/gettext.git/commit/?id=10af7fe6bd
2. <2ce9ec406501d112e032c8208417f8100bed04c6.1397712142.git.worldhello.net@gmail.com>
   (https://public-inbox.org/git/2ce9ec406501d112e032c8208417f8100bed04c6.1397712142.git.worldhello.net@gmail.com/)
3. https://lists.gnu.org/archive/html/bug-gettext/2014-04/msg00016.html

Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
Acked-by: Jiang Xin <worldhello.net@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>