i18n: git-checkout "HEAD is now at" message

Gettextize the "HEAD is now at" messages. Several tests in t7201-co.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>

builtin/checkout.c

@@ -571,7 +571,7 @@ static void update_refs_for_switch(struct checkout_opts *opts,
 		if (!opts->quiet) {
 			if (old->path && advice_detached_head)
 				detach_advice(old->path, new->name);
-			describe_detached_head("HEAD is now at", new->commit);
+			describe_detached_head(_("HEAD is now at"), new->commit);
 		}
 	}
 	remove_branch_state();

t/t7201-co.sh

@@ -223,7 +223,7 @@ test_expect_success 'checkout --merge --conflict=diff3 <branch>' '
 	test_cmp two expect
 '
 
-test_expect_success 'checkout to detach HEAD (with advice declined)' '
+test_expect_success C_LOCALE_OUTPUT 'checkout to detach HEAD (with advice declined)' '
 
 	git config advice.detachedHead false &&
 	git checkout -f renamer && git clean -f &&
@@ -242,7 +242,7 @@ test_expect_success 'checkout to detach HEAD (with advice declined)' '
 	fi
 '
 
-test_expect_success 'checkout to detach HEAD' '
+test_expect_success C_LOCALE_OUTPUT 'checkout to detach HEAD' '
 	git config advice.detachedHead true &&
 	git checkout -f renamer && git clean -f &&
 	git checkout renamer^ 2>messages &&
@@ -260,7 +260,7 @@ test_expect_success 'checkout to detach HEAD' '
 	fi
 '
 
-test_expect_success 'checkout to detach HEAD with branchname^' '
+test_expect_success C_LOCALE_OUTPUT 'checkout to detach HEAD with branchname^' '
 
 	git checkout -f master && git clean -f &&
 	git checkout renamer^ &&
@@ -276,7 +276,7 @@ test_expect_success 'checkout to detach HEAD with branchname^' '
 	fi
 '
 
-test_expect_success 'checkout to detach HEAD with :/message' '
+test_expect_success C_LOCALE_OUTPUT 'checkout to detach HEAD with :/message' '
 
 	git checkout -f master && git clean -f &&
 	git checkout ":/Initial" &&
@@ -292,7 +292,7 @@ test_expect_success 'checkout to detach HEAD with :/message' '
 	fi
 '
 
-test_expect_success 'checkout to detach HEAD with HEAD^0' '
+test_expect_success C_LOCALE_OUTPUT 'checkout to detach HEAD with HEAD^0' '
 
 	git checkout -f master && git clean -f &&
 	git checkout HEAD^0 &&