Correct git-annex info to include unlocked files in v6 repository.

An unlocked present file does not have a pointer file in the worktree, so
info skipped counting it.

It may be that unused was also affected by the problem, but it seemed not
to be in my tests. I think because of the use of the associatedFilesFilter.

This fix slows down both info and unused a little bit, since they have to
query the contents of files from git, but only when handling unlocked files.

Annex/Link.hs

@@ -159,7 +159,9 @@ formatPointer :: Key -> String
 formatPointer k = 
 	toInternalGitPath (pathSeparator:objectDir </> keyFile k) ++ "\n"
 
-{- Checks if a file is a pointer to a key. -}
+{- Checks if a worktree file is a pointer to a key.
+ -
+ - Unlocked files whose content is present are not detected by this. -}
 isPointerFile :: FilePath -> IO (Maybe Key)
 isPointerFile f = catchDefaultIO Nothing $ do
 	b <- L.take maxPointerSz <$> L.readFile f