updated changelog as a part of the release

git-svn-id: https://hudson.dev.java.net/svn/hudson/trunk/hudson/main@11701 71c3de6d-444a-0410-be80-ed276b4c234a

debian/changelog

+hudson (1.251) unstable; urgency=low
+
+  * See http://hudson.dev.java.net/changelog.html for more details.
+
+ -- Kohsuke Kawaguchi <kk@kohsuke.org>  Fri, 22 Aug 2008 18:08:18 -0700
+
 hudson (1.250) unstable; urgency=low
 
   * See http://hudson.dev.java.net/changelog.html for more details.