Sync with v2.9.1

* maint:
Git 2.9.1

diff --combined Documentation/git.txt
index 38c3da2f7d3fa21506ebd553d3ed2ac311ab4a39,a474fa1a21f1a9d0ec2be3ad10a548bbb3b1a9b0..bb324358742e3aedba35874e687682b3bfd2fcfd
--- 1/Documentation/git.txt
--- 2/Documentation/git.txt
+++ b/Documentation/git.txt
@@@ -43,9 -43,10 +43,10 @@@ unreleased) version of Git, that is ava
  branch of the `git.git` repository.
  Documentation for older releases are available here:
  
- * link:v2.9.0/git.html[documentation for release 2.9]
+ * link:v2.9.1/git.html[documentation for release 2.9.1]
  
  * release notes for
+   link:RelNotes/2.9.1.txt[2.9.1],
    link:RelNotes/2.9.0.txt[2.9].
  
  * link:v2.8.4/git.html[documentation for release 2.8.4]
@@@ -1083,14 -1084,6 +1084,14 @@@ of clones and fetches
        cloning of shallow repositories.
        See `GIT_TRACE` for available trace output options.
  
 +`GIT_TRACE_CURL`::
 +      Enables a curl full trace dump of all incoming and outgoing data,
 +      including descriptive information, of the git transport protocol.
 +      This is similar to doing curl `--trace-ascii` on the command line.
 +      This option overrides setting the `GIT_CURL_VERBOSE` environment
 +      variable.
 +      See `GIT_TRACE` for available trace output options.
 +
  `GIT_LITERAL_PATHSPECS`::
        Setting this variable to `1` will cause Git to treat all
        pathspecs literally, rather than as glob patterns. For example,