Put non-object tmp files in .git/annex/misctmp, leaving .git/annex/tmp for only partially transferred objects.

This allows eg, putting .git/annex/tmp on a ram disk, if the disk IO
of temp object files is too annoying (and if you don't want to keep
partially transferred objects across reboots).

.git/annex/misctmp must be on the same filesystem as the git work tree,
since files are moved to there in a way that will not work cross-device,
as well as symlinked into there.

I first wanted to put the tmp objects in .git/annex/objects/tmp, but
that would pose transition problems on upgrade when partially transferred
objects existed.

git annex info does not currently show the size of .git/annex/misctemp,
since it should stay small. It would also be ok to make something clean it
out, periodically.

Annex/ReplaceFile.hs

@@ -24,7 +24,7 @@ import Annex.Exception
  -}
 replaceFile :: FilePath -> (FilePath -> Annex ()) -> Annex ()
 replaceFile file a = do
-	tmpdir <- fromRepo gitAnnexTmpDir
+	tmpdir <- fromRepo gitAnnexTmpMiscDir
 	void $ createAnnexDirectory tmpdir
 	bracketIO (setup tmpdir) nukeFile $ \tmpfile -> do
 		a tmpfile
@@ -36,4 +36,4 @@ replaceFile file a = do
 		return tmpfile
 	fallback tmpfile _ = do
 		createDirectoryIfMissing True $ parentDir file
-		rename tmpfile file
+		moveFile tmpfile file