Sync with 2.5.1

diff --combined Documentation/git.txt
index 2795340fb2e793b51f775e79defe52453adcdc9d,5a78d77533f18c96a0fbee7ac97ba8478eb169ca..4e5d55be6a2b5db801e651b054160b393e148576
--- 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:v2.5.0/git.html[documentation for release 2.5]
+ * link:v2.5.1/git.html[documentation for release 2.5.1]
  
  * release notes for
+   link:RelNotes/2.5.1.txt[2.5.1],
    link:RelNotes/2.5.0.txt[2.5].
  
  * link:v2.4.8/git.html[documentation for release 2.4.8]
@@@ -1010,20 -1011,9 +1011,20 @@@ Unsetting the variable, or setting it t
        Enables trace messages for all packets coming in or out of a
        given program. This can help with debugging object negotiation
        or other protocol issues. Tracing is turned off at a packet
 -      starting with "PACK".
 +      starting with "PACK" (but see 'GIT_TRACE_PACKFILE' below).
        See 'GIT_TRACE' for available trace output options.
  
 +'GIT_TRACE_PACKFILE'::
 +      Enables tracing of packfiles sent or received by a
 +      given program. Unlike other trace output, this trace is
 +      verbatim: no headers, and no quoting of binary data. You almost
 +      certainly want to direct into a file (e.g.,
 +      `GIT_TRACE_PACKFILE=/tmp/my.pack`) rather than displaying it on
 +      the terminal or mixing it with other trace output.
 ++
 +Note that this is currently only implemented for the client side
 +of clones and fetches.
 +
  'GIT_TRACE_PERFORMANCE'::
        Enables performance related trace messages, e.g. total execution
        time of each Git command.