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/t5604-clone-reference.sh

@@ -175,7 +175,7 @@ test_expect_success 'clone using repo pointed at by gitfile as reference' '
 test_expect_success 'clone and dissociate from reference' '
 	git init P &&
 	(
-		cd P &&	test_commit one
+		cd P && test_commit one
 	) &&
 	git clone P Q &&
 	(
@@ -326,15 +326,16 @@ test_expect_success SYMLINKS 'clone repo with symlinked or unknown files at obje
 	for raw in $(ls T*.raw)
 	do
 		sed -e "s!/../!/Y/!; s![0-9a-f]\{38,\}!Z!" -e "/commit-graph/d" \
-		    -e "/multi-pack-index/d" <$raw >$raw.de-sha || return 1
+		    -e "/multi-pack-index/d" <$raw >$raw.de-sha-1 &&
+		sort $raw.de-sha-1 >$raw.de-sha || return 1
 	done &&
 
 	cat >expected-files <<-EOF &&
 	./Y/Z
 	./Y/Z
+	./Y/Z
 	./a-loose-dir/Z
 	./an-object
-	./Y/Z
 	./info/packs
 	./pack/pack-Z.idx
 	./pack/pack-Z.pack