merge(3p/git): Merge git subtree at v2.29.2

This also bumps the stable nixpkgs to 20.09 as of 2020-11-21, because
there is some breakage in the git build related to the netrc
credentials helper which someone has taken care of in nixpkgs.

The stable channel is not used for anything other than git, so this
should be fine.

Change-Id: I3575a19dab09e1e9556cf8231d717de9890484fb

third_party/git/t/t5313-pack-bounds-checks.sh

@@ -38,16 +38,26 @@ munge () {
 # for the initial, and another ofs(4*nr) past that for the extended.
 #
 ofs_table () {
-	echo $((4 + 4 + 4*256 + 20*$1 + 4*$1))
+	echo $((4 + 4 + 4*256 + $(test_oid rawsz)*$1 + 4*$1))
 }
 extended_table () {
 	echo $(($(ofs_table "$1") + 4*$1))
 }
 
+test_expect_success 'setup' '
+	test_oid_cache <<-EOF
+	oid000 sha1:1485
+	oid000 sha256:4222
+
+	oidfff sha1:74
+	oidfff sha256:1350
+	EOF
+'
+
 test_expect_success 'set up base packfile and variables' '
 	# the hash of this content starts with ff, which
 	# makes some later computations much simpler
-	echo 74 >file &&
+	echo $(test_oid oidfff) >file &&
 	git add file &&
 	git commit -m base &&
 	git repack -ad &&
@@ -140,10 +150,10 @@ test_expect_success 'bogus offset inside v2 extended table' '
 	# an extended table (if the first object were larger than 2^31).
 	#
 	# Note that the value is important here. We want $object as
-	# the second entry in sorted-sha1 order. The sha1 of 1485 starts
+	# the second entry in sorted-hash order. The hash of this object starts
 	# with "000", which sorts before that of $object (which starts
 	# with "fff").
-	second=$(echo 1485 | git hash-object -w --stdin) &&
+	second=$(test_oid oid000 | git hash-object -w --stdin) &&
 	do_pack "$object $second" --index-version=2 &&
 
 	# We have to make extra room for the table, so we cannot