Merge branch 'ah/format-patch-thread-doc'

Doc update.

* ah/format-patch-thread-doc:
  format-patch: correct documentation of --thread without an argument

diff --cc Documentation/git-format-patch.txt
Simple merge

diff --cc t/t4014-format-patch.sh
index 7f1d4e8d585f0008ba8d7383d3eb46c4994304e5,b27a72f78a81b7bc438d552f625de1204fe43214..3cf2b7a7fb70ec272d9f12294a26e2a1685c5999
--- 1/t/t4014-format-patch.sh
--- 2/t/t4014-format-patch.sh
+++ b/t/t4014-format-patch.sh
@@@ -470,9 -470,14 +470,14 @@@ test_expect_success 'thread' 
        check_threading expect.thread --thread main
  '
  
+ test_expect_success '--thread overrides format.thread=deep' '
+       test_config format.thread deep &&
+       check_threading expect.thread --thread main
+ '
+ 
  cat >expect.in-reply-to <<EOF
  ---
 -Message-Id: <0>
 +Message-ID: <0>
  In-Reply-To: <1>
  References: <1>
  ---