t4151: consolidate multiple calls to test_i18ngrep

Attempting to grep the output of test_i18ngrep will not work under a
poison build, since the output is (almost) guaranteed not to have the
string you are looking for. In this case, we have a test_i18ngrep call
which attempts to filter the contents of a file, which was itself the
result of a call to test_i18ngrep. In this case, we can achieve the
same effect with a single call to test_i18ngrep (without creating the
intermediate file), since the second regular expression can be used
without change to filter the original input.

Also, replace a call to test_i18ncmp with test_cmp, since the content
being compared is not subject to i18n anyway.

Signed-off-by: Ramsay Jones <ramsay@ramsayjones.plus.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

t/t4151-am-abort.sh

@@ -46,9 +46,8 @@ do
 
 	test_expect_success "am$with3 --skip continue after failed am$with3" '
 		test_must_fail git am$with3 --skip >output &&
-		test_i18ngrep "^Applying" output >output.applying &&
+		test_i18ngrep "^Applying: 6$" output &&
-		test_i18ngrep "^Applying: 6$" output.applying &&
+		test_cmp file-2-expect file-2 &&
-		test_i18ncmp file-2-expect file-2 &&
 		test ! -f .git/MERGE_RR
 	'