Merge into a single US-exportable libcrypt, which only provides

Merge into a single US-exportable libcrypt, which only provides
one-way hash functions for authentication purposes.  There is no more
"set the libcrypt->libXXXcrypt" nightmare.
- Undo the libmd.so hack, use -D to hide the md5c.c internals.
- Remove the symlink hacks in release/Makefile
- the algorthm is set by set_crypt_format() as before.  If this is
  not called, it tries to heuristically figure out the hash format, and
  if all else fails, it uses the optional auth.conf entry to chose the
  overall default hash.
- Since source has non-hidden crypto in it there may be some issues with
  having the source it in some countries, so preserve the "secure/*"
  division.  You can still build a des-free libcrypt library if you want
  to badly enough.  This should not be a problem in the US or exporting
  from the US as freebsd.org had notified BXA some time ago.  That makes
  this stuff re-exportable by anyone.
- For consistancy, the default in absence of any other clues is md5.  This
  is to try and minimize POLA across buildworld where folk may suddenly
  be activating des-crypt()-hash support.  Since the des hash may not
  always be present, it seemed sensible to make the stronger md5 algorithm
  the default.
All things being equal, no functionality is lost.

Reviewed-by: jkh
(flame-proof suit on)