convert renameFile to moveFile to support cross-device moves

Improve handling of some .git/annex/ subdirectories being on other
filesystems, in the bittorrent special remote, and youtube-dl integration,
and git-annex addurl.

The only one of these that I've confirmed to be a problem is in the
bittorrent special remote when .git/annex/tmp and .git/annex/othertmp are
on different filesystems.

As well as auditing for renameFile, also audited for createLink, all of
those are ok as are the other remaining renameFile calls. Also audited all
code paths that use .git/annex/othertmp, and did not find any other
cross-device problems. So, removing mention of othertmp needing to be on
the same device.

Sponsored-by: Dartmouth College's Datalad project

Remote/BitTorrent.hs

@@ -217,7 +217,7 @@ downloadTorrentFile u = do
 						ok <- Url.withUrlOptions $ 
 							Url.download nullMeterUpdate Nothing u f
 						when ok $
-							liftIO $ renameFile f (fromRawFilePath torrent)
+							liftIO $ moveFile (toRawFilePath f) torrent
 						return ok
 		)
 
@@ -228,7 +228,7 @@ downloadMagnetLink u metadir dest = ifM download
 			<$> dirContents metadir
 		case ts of
 			(t:[]) -> do
-				renameFile t dest
+				moveFile (toRawFilePath t) (toRawFilePath dest)
 				return True
 			_ -> return False
 	, return False
@@ -256,7 +256,7 @@ downloadTorrentContent k u dest filenum p = do
 		showOutput
 		ifM (download torrent downloaddir <&&> liftIO (doesFileExist dlf))
 			( do
-				liftIO $ renameFile dlf dest
+				liftIO $ moveFile (toRawFilePath dlf) (toRawFilePath dest)
 				-- The downloaddir is not removed here,
 				-- so if aria downloaded parts of other
 				-- files, and this is called again, it will