[debian/changelog] add a Closes tag to mvo's --only-source patch

debian/changelog

@@ -3,7 +3,7 @@ apt (0.7.23) unstable; urgency=low
   [ Michael Vogt ]
   * cmdline/apt-get.cc:
     - honor APT::Get::Only-Source properly in FindSrc() (thanks to
-      Martin Pitt for reporting the problem)
+      Martin Pitt for reporting the problem) (Closes: #535362)
 
   [ David Kalnischkies ]
   * cmdline/apt-get.cc: