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

Command/AddUrl.hs

@@ -467,9 +467,7 @@ addWorkTree _ addunlockedmatcher u url file key mtmp = case mtmp of
 		-- Move to final location for large file check.
 		pruneTmpWorkDirBefore tmp $ \_ -> do
 			createWorkTreeDirectory (P.takeDirectory file)
-			liftIO $ renameFile 
-				(fromRawFilePath tmp)
-				(fromRawFilePath file)
+			liftIO $ moveFile tmp file
 		largematcher <- largeFilesMatcher
 		large <- checkFileMatcher largematcher file
 		if large
@@ -477,9 +475,7 @@ addWorkTree _ addunlockedmatcher u url file key mtmp = case mtmp of
 				-- Move back to tmp because addAnnexedFile
 				-- needs the file in a different location
 				-- than the work tree file.
-				liftIO $ renameFile
-					(fromRawFilePath file)
-					(fromRawFilePath tmp)
+				liftIO $ moveFile file tmp
 				go
 			else Command.Add.addSmall (DryRun False) file s
 				>>= maybe noop void