Document the current behaviour of the DES interface.

     projects.  The old libdes interface is provided, as well as crypt(),

     if openssl/des_old.h is included.  Note that crypt() is no longer

     declared in openssl/des.h.

     In order to maintain compatibility with current applications using

     libcrypto, the old libdes interface is still provided, as long as

     OPENSSL_NO_OLD_DES_SUPPORT is not defined, by automatically including

     openssl/des_old.h. 

     NOTE: This is a major break of an old API into a new one.  Software

     authors are encouraged to switch to the DES_ style functions.  Some