the docs to reflect this change and correct libeay.num.

libdes (which is still used out there) or other des implementations,
the OpenSSL DES functions are renamed to begin with DES_ instead of
des_.  Compatibility routines are provided and declared by including
openssl/des_old.h.  Those declarations are the same as were in des.h
when the OpenSSL project started, which is exactly how libdes looked
at that time, and hopefully still looks today.

The compatibility functions will be removed in some future release, at
the latest in version 1.0.

Avoid enabled 'assert()' in production library.

used anywhere in OpenSSL, but might be used by libdes applications.

Never use des_set_key (it depends on the global variable des_check_key),
but usually des_set_key_unchecked.
Only destest.c bothered to look at the return values of des_set_key,
but it did not set des_check_key -- if it had done so,
most checks would have failed because of wrong parity and
because of weak keys.

(meaning pointer to char) to des_cblock * (meaning pointer to
array with 8 char elements), which allows the compiler to
do more typechecking.  (The changed argument types were of type
des_cblock * back in SSLeay, and a lot of ugly casts were
used then to turn them into pointers to elements; but it can be
done without those casts.)

Introduce new type const_des_cblock -- before, the pointers rather
than the elements pointed to were declared const, and for
some reason gcc did not complain about this (but some other
compilers did).