Reserve px_get_random_bytes() for strong randomness,
add new function px_get_pseudo_random_bytes() for
weak randomness and use it in gen_salt().

On openssl case, use RAND_pseudo_bytes() for
px_get_pseudo_random_bytes().

Final result is that is user has not configured random
souce but kept the 'silly' one, gen_salt() keeps
working, but pgp_encrypt() will throw error.

Marko Kreen