Merge branch 'lh/send-email-hide-x-mailer'

"git send-email" normally identifies itself via X-Mailer: header
in the message it sends out.  A new command line flag allows the
user to squelch the header.

* lh/send-email-hide-x-mailer:
  test/send-email: --[no-]xmailer tests
  send-email: add --[no-]xmailer option

Documentation/config.txt

@@ -2329,6 +2329,7 @@ sendemail.smtpuser::
 sendemail.thread::
 sendemail.transferencoding::
 sendemail.validate::
+sendemail.xmailer::
 	See linkgit:git-send-email[1] for description.
 
 sendemail.signedoffcc::

Documentation/git-send-email.txt

@@ -141,6 +141,11 @@ Note that no attempts whatsoever are made to validate the encoding.
 	configuration value; if that is unspecified, git will use 8bit and not
 	add a Content-Transfer-Encoding header.
 
+--xmailer::
+--no-xmailer::
+	Add (or prevent adding) the "X-Mailer:" header.  By default,
+	the header is added, but it can be turned off by setting the
+	`sendemail.xmailer` configuration variable to `false`.
 
 Sending
 ~~~~~~~