makefs: Sort directory contents by name (Jan-Benedict Glaw)

`makefs` inserts nodes into its internal data structures in the order as
returned by `readdir()` calls. As this is unpredictable, sort entries by
name before creating the target filesystem.

  This is done by first converting the (per-directory) linked list into
a plain array, sort it, finally re-link the list. Special case for the
sorting function: The "." directory entry seems to be ment to be always
at the front, so always check that first.

(christos)