type const uint8_t * (was const des_cblock *).

* des-compat.h (const_des_cblock): New bogus type. Disabled use of
const, for compatibility with openssl.

Rev: src/nettle/des-compat.c:1.14
Rev: src/nettle/des-compat.h:1.12
Rev: src/nettle/testsuite/des-compat-test.c:1.7