i18n: git-commit "middle of a merge" message

Gettextize the "You are in the middle of a merge -- cannot amend."
message. Several tests in t7110-reset-merge.sh explicitly checked for
this message. Change them to skip under GETTEXT_POISON=YesPlease.

Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
diff --git a/builtin/commit.c b/builtin/commit.c
index 472c2ba..e944c4d 100644
--- a/builtin/commit.c
+++ b/builtin/commit.c
@@ -928,9 +928,9 @@
 	if (amend && initial_commit)
 		die(_("You have nothing to amend."));
 	if (amend && in_merge)
-		die("You are in the middle of a merge -- cannot amend.");
+		die(_("You are in the middle of a merge -- cannot amend."));
 	if (fixup_message && squash_message)
-		die("Options --squash and --fixup cannot be used together");
+		die(_("Options --squash and --fixup cannot be used together"));
 	if (use_message)
 		f++;
 	if (edit_message)