i18n: Rewrite gettext messages start with dash

Gettext message in a shell script should not start with '-', one
workaround is adding '--' between gettext and the message, like:

    gettext -- "--exec option ..."

But due to a bug in the xgettext extraction, xgettext can not
extract the actual message for this case. Rewriting the message
is a simpler and better solution.

Reported-by: Vincent van Ravesteijn <vfr@lyx.org>
Signed-off-by: Jiang Xin <worldhello.net@gmail.com>
Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
Reviewed-by: Stefano Lattarini <stefano.lattarini@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

git-rebase.sh

@@ -317,7 +317,7 @@ test $# -gt 2 && usage
 if test -n "$cmd" &&
    test "$interactive_rebase" != explicit
 then
-	die "$(gettext -- "--exec option must be used with --interactive option")"
+	die "$(gettext "The --exec option must be used with the --interactive option")"
 fi
 
 if test -n "$action"

git-submodule.sh

@@ -746,7 +746,7 @@ cmd_summary() {
 	if [ -n "$files" ]
 	then
 		test -n "$cached" &&
-		die "$(gettext -- "--cached cannot be used with --files")"
+		die "$(gettext "The --cached option cannot be used with the --files option")"
 		diff_cmd=diff-files
 		head=
 	fi

t/t3404-rebase-interactive.sh

@@ -858,7 +858,7 @@ test_expect_success 'rebase -ix with --autosquash' '
 test_expect_success 'rebase --exec without -i shows error message' '
 	git reset --hard execute &&
 	test_must_fail git rebase --exec "git show HEAD" HEAD~2 2>actual &&
-	echo "--exec option must be used with --interactive option" >expected &&
+	echo "The --exec option must be used with the --interactive option" >expected &&
 	test_i18ncmp expected actual
 '