merge(third_party/git): Merge squashed git subtree at v2.23.0

Merge commit '1b593e1ea4' as 'third_party/git'

third_party/git/t/t4044-diff-index-unique-abbrev.sh

@@ -0,0 +1,41 @@
+#!/bin/sh
+
+test_description='test unique sha1 abbreviation on "index from..to" line'
+. ./test-lib.sh
+
+if ! test_have_prereq SHA1
+then
+       skip_all='not using SHA-1 for objects'
+       test_done
+fi
+
+cat >expect_initial <<EOF
+100644 blob 51d2738463ea4ca66f8691c91e33ce64b7d41bb1	foo
+EOF
+
+cat >expect_update <<EOF
+100644 blob 51d2738efb4ad8a1e40bed839ab8e116f0a15e47	foo
+EOF
+
+test_expect_success 'setup' '
+	echo 4827 > foo &&
+	git add foo &&
+	git commit -m "initial" &&
+	git cat-file -p HEAD: > actual &&
+	test_cmp expect_initial actual &&
+	echo 11742 > foo &&
+	git commit -a -m "update" &&
+	git cat-file -p HEAD: > actual &&
+	test_cmp expect_update actual
+'
+
+cat >expect <<EOF
+index 51d27384..51d2738e 100644
+EOF
+
+test_expect_success 'diff does not produce ambiguous index line' '
+	git diff HEAD^..HEAD | grep index > actual &&
+	test_cmp expect actual
+'
+
+test_done