grep: use memmem() for fixed string search

Allow searching beyond NUL characters by using memmem() instead of
strstr().

Signed-off-by: Rene Scharfe <rene.scharfe@lsrfire.ath.cx>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
diff --git a/t/t7008-grep-binary.sh b/t/t7008-grep-binary.sh
index 4a12d97..9adc9ed 100755
--- a/t/t7008-grep-binary.sh
+++ b/t/t7008-grep-binary.sh
@@ -51,4 +51,8 @@
 	test_cmp expect actual
 '
 
+test_expect_success 'git grep -F ile a' '
+	git grep -F ile a
+'
+
 test_done