short-circuit as soon as enough remotes are verified to have a file

Backend/File.hs

@@ -111,6 +111,9 @@ checkRemoveKey key = do
 				then return True
 				else notEnoughCopies need have bad
 		findcopies need have (r:rs) bad = do
+			if (have >= need)
+				then return True
+				else do
 					haskey <- Remotes.inAnnex r key
 					case (haskey) of
 						Right True	-> findcopies need (have+1) rs bad