merge(3p/git): Merge git subtree at v2.29.2 r/1890

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

1 files changed, 17 insertions, 0 deletions

diff --git a/third_party/git/t/t4018/markdown-heading-non-headings b/third_party/git/t/t4018/markdown-heading-non-headings
new file mode 100644
index 000000000000..c479c1a3f1e2
--- /dev/null
+++ b/third_party/git/t/t4018/markdown-heading-non-headings
@@ -0,0 +1,17 @@
+Headings can be right next to other lines of the file:
+# RIGHT
+Indents of four or more spaces make a code block:
+
+    # code comment, not heading
+
+If there's no space after the final hash, it's not a heading:
+
+#hashtag
+
+Sequences of more than 6 hashes don't make a heading:
+
+####### over-enthusiastic heading
+
+So the detected heading should be right up at the start of this file.
+
+ChangeMe