[directory] status of HsDirectory.h

[Phil Ruffwind]

I noticed that there aren't many things left in the HsDirectory.h:

  - macros from autoconf
  - __hscore_long_path_size
  - __hscore_S_IRUSR/IWUSR/IXUSR/IFDIR

Most of these could be done easily using hsc so I was tempted to
remove them.  Not to mention, the implementation of
__hscore_long_path_size is rather dangerous on systems where PATH_MAX
is not defined.[1]

However, I wonder if the __hscore prefix has any significance.  Are
these functions by any chance used in GHC internals or some other
libraries?

For now I intend to leave them as is.  But if no-one else uses them,
then I think the header should be deprecated and made private in the
future.

[1]: http://pubs.opengroup.org/onlinepubs/9699919799

--
Phil