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/lib-log-graph.sh

@@ -0,0 +1,28 @@
+# Helps shared by the test scripts for comparing log graphs.
+
+sanitize_log_output () {
+	sed -e 's/ *$//' \
+	    -e 's/commit [0-9a-f]*$/commit COMMIT_OBJECT_NAME/' \
+	    -e 's/Merge: [ 0-9a-f]*$/Merge: MERGE_PARENTS/' \
+	    -e 's/Merge tag.*/Merge HEADS DESCRIPTION/' \
+	    -e 's/Merge commit.*/Merge HEADS DESCRIPTION/' \
+	    -e 's/index [0-9a-f]*\.\.[0-9a-f]*/index BEFORE..AFTER/'
+}
+
+lib_test_cmp_graph () {
+	git log --graph "$@" >output &&
+	sed 's/ *$//' >output.sanitized <output &&
+	test_i18ncmp expect output.sanitized
+}
+
+lib_test_cmp_short_graph () {
+	git log --graph --pretty=short "$@" >output &&
+	sanitize_log_output >output.sanitized <output &&
+	test_i18ncmp expect output.sanitized
+}
+
+lib_test_cmp_colored_graph () {
+	git log --graph --color=always "$@" >output.colors.raw &&
+	test_decode_color <output.colors.raw | sed "s/ *\$//" >output.colors &&
+	test_cmp expect.colors output.colors
+}