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/url.c

@@ -5,7 +5,7 @@ int is_urlschemechar(int first_flag, int ch)
 {
 	/*
 	 * The set of valid URL schemes, as per STD66 (RFC3986) is
-	 * '[A-Za-z][A-Za-z0-9+.-]*'. But use sightly looser check
+	 * '[A-Za-z][A-Za-z0-9+.-]*'. But use slightly looser check
 	 * of '[A-Za-z0-9][A-Za-z0-9+.-]*' because earlier version
 	 * of check used '[A-Za-z0-9]+' so not to break any remote
 	 * helpers.
@@ -86,6 +86,12 @@ char *url_decode_mem(const char *url, int len)
 	return url_decode_internal(&url, len, NULL, &out, 0);
 }
 
+char *url_percent_decode(const char *encoded)
+{
+	struct strbuf out = STRBUF_INIT;
+	return url_decode_internal(&encoded, strlen(encoded), NULL, &out, 0);
+}
+
 char *url_decode_parameter_name(const char **query)
 {
 	struct strbuf out = STRBUF_INIT;