info: Fix "backend usage" numbers, which were counting present keys twice.

Let's just count the referenced keys for that, and not present keys at all.

Command/Info.hs

@@ -403,11 +403,8 @@ disk_size = simpleStat "available local disk space" $
 
 backend_usage :: Stat
 backend_usage = stat "backend usage" $ json fmt $
-	calc
-		<$> (backendsKeys <$> cachedReferencedData)
-		<*> (backendsKeys <$> cachedPresentData)
+	sort . M.toList . backendsKeys <$> cachedReferencedData
   where
-	calc x y = sort $ M.toList $ M.unionWith (+) x y
 	fmt = multiLine . map (\(n, b) -> b ++ ": " ++ show n) . map swap
 
 numcopies_stats :: Stat

debian/changelog

@@ -33,6 +33,8 @@ git-annex (6.20151219) UNRELEASED; urgency=medium
   * Debian: Adjust build dependencies for webapp, DAV. Now available on
     mips, mipsel, but temporarily removed armel since build is failing
     there.
+  * info: Fix "backend usage" numbers, which were counting present keys
+    twice.
 
  -- Joey Hess <id@joeyh.name>  Sat, 19 Dec 2015 13:31:17 -0400