optimise fsck --from normal git remotes

For a local git remote, can symlink the file.
For a git remote using rsync, can preseed any local content.

There are a few reasons to use fsck --from on a normal git remote.
One is if it's using gitosis or similar, and you don't have shell access
to run git annex locally. Another reason could be if you just want to
fsck certian files of a bare remote.

Remote/Rsync.hs

@@ -19,8 +19,6 @@ import Remote.Helper.Special
 import Remote.Helper.Encryptable
 import Crypto
 import Utility.RsyncFile
-import Utility.CopyFile
-import Utility.FileMode
 
 type RsyncUrl = String
 
@@ -106,20 +104,13 @@ storeEncrypted o (cipher, enck) k = withTmp enck $ \tmp -> do
 
 retrieve :: RsyncOpts -> Key -> Bool -> FilePath -> Annex Bool
 retrieve o k tmp f = untilTrue (rsyncUrls o k) $ \u -> do
-	when tmp $ preseed
+	when tmp $ preseedTmp k f
 	rsyncRemote o
 		-- use inplace when retrieving to support resuming
 		[ Param "--inplace"
 		, Param u
 		, Param f
 		]
-	where
-		-- this speeds up fsck --from
-		preseed = unlessM (liftIO $ doesFileExist f) $
-			whenM (inAnnex k) $ do
-				s <- inRepo $ gitAnnexLocation k
-				liftIO $ whenM (copyFileExternal s f) $
-					allowWrite f
 
 retrieveEncrypted :: RsyncOpts -> (Cipher, Key) -> FilePath -> Annex Bool
 retrieveEncrypted o (cipher, enck) f = withTmp enck $ \tmp -> do