debian: Do not emit tar warnings from dpkg cron file

Ref: #745592, #745651

debian/changelog

@@ -1,7 +1,7 @@
 dpkg (1.17.8) UNRELEASED; urgency=low
 
   * Do not backup nonexistent database files from the cron.daily file.
-    Closes: #745592, #745651
+    And stop emitting tar warnings. Closes: #745592, #745651
 
  -- Guillem Jover <guillem@debian.org>  Mon, 21 Apr 2014 17:59:10 +0200
 

debian/dpkg.cron.daily

@@ -25,8 +25,9 @@ if cd /var/backups ; then
     # The alternatives database is independent from the dpkg database.
     dbalt=alternatives
     if ! test -e ${dbalt}.tar.0 ||
-       ! tar -df ${dbalt}.tar.0 -C $dbdir $dbalt >/dev/null ; then
-        tar -cf ${dbalt}.tar -C $dbdir $dbalt
+       ! tar -df ${dbalt}.tar.0 --warning=none -C $dbdir $dbalt >/dev/null ;
+    then
+        tar -cf ${dbalt}.tar --warning=none -C $dbdir $dbalt
         savelog -c 7 -J ${dbalt}.tar >/dev/null
     fi
 fi