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/Migrate.hs

@@ -63,7 +63,7 @@ perform file oldkey oldbackend newbackend = do
 	go newkey = stopUnless (Command.ReKey.linkKey oldkey newkey) $
 		next $ Command.ReKey.cleanup file oldkey newkey
 	genkey = do
-		content <- inRepo $ gitAnnexLocation oldkey
+		content <- calcRepo $ gitAnnexLocation oldkey
 		let source = KeySource
 			{ keyFilename = file
 			, contentLocation = content