[debian/changlog] add entry for the "missing source.list file" fix

* apt-pkg/sourcelist.cc:
  - only show warning about missing sources.list file if no we have
    no valid sourceentry (Closes: #539731)

debian/changelog

@@ -13,6 +13,9 @@ apt (0.7.23) unstable; urgency=low
   * apt-pkg/contrib/strutl.cc:
     - enable thousand separator according to the current locale
       (by Luca Bruno, Closes: #223712)
+  * apt-pkg/sourcelist.cc:
+    - only show warning about missing sources.list file if no we have
+      no valid sourceentry (Closes: #539731)
 
  -- Michael Vogt <michael.vogt@ubuntu.com>  Thu, 30 Jul 2009 15:27:30 +0200