Use lower case hash directories for storing files on crippled filesystems, same as is already done for bare repositories.

* since this is a crippled filesystem anyway, git-annex doesn't use
  symlinks on it
* so there's no reason to use the mixed case hash directories that we're
  stuck using to avoid breaking everyone's symlinks to the content
* so we can do what is already done for all bare repos, and make non-bare
  repos on crippled filesystems use the all-lower case hash directories
* which are, happily, all 3 letters long, so they cannot conflict with
  mixed case hash directories
* so I was able to 100% fix this and even resuming `git annex add` in the
  test case will recover and it will all just work.

Command/ReKey.hs

@@ -49,7 +49,7 @@ perform file oldkey newkey = do
 {- Make a hard link to the old key content, to avoid wasting disk space. -}
 linkKey :: Key -> Key -> Annex Bool
 linkKey oldkey newkey = getViaTmpUnchecked newkey $ \tmp -> do
-	src <- inRepo $ gitAnnexLocation oldkey
+	src <- calcRepo $ gitAnnexLocation oldkey
 	ifM (liftIO $ doesFileExist tmp)
 		( return True
 		, ifM crippledFileSystem