remove optimize subcommand; use --auto instead

get, drop: Added --auto option, which decides whether to get/drop content
as needed to work toward the configured numcopies.

The problem with bundling it up in optimize was that I then found I wanted
to run an optmize that did not drop files, only got them. Considered adding
a --only-get switch to it, but that seemed wrong. Instead, let's make
existing subcommands optionally smarter.

Note that the only actual difference between drop and drop --auto is that
the latter does not even try to drop a file if it knows of not enough
copies, and does not print any error messages about files it was unable to
drop.

It might be nice to make get avoid asking git for attributes when not in
auto mode. For now it always asks for attributes.

Command/Drop.hs

@@ -29,13 +29,15 @@ seek = [withNumCopies start]
 {- Indicates a file's content is not wanted anymore, and should be removed
  - if it's safe to do so. -}
 start :: CommandStartAttrFile
-start (file, numcopies) = isAnnexed file $ \(key, _) -> do
+start (file, attr) = isAnnexed file $ \(key, _) -> do
 	present <- inAnnex key
 	if present
-		then do
+		then autoCopies key (>) numcopies $ do
 			showStart "drop" file
-			next $ perform key $ readMaybe numcopies
+			next $ perform key numcopies
 		else stop
+	where
+		numcopies = readMaybe attr
 
 perform :: Key -> Maybe Int -> CommandPerform
 perform key numcopies = do