BN_new() and BN_secure_new() not only allocate memory, but also
initialise it to deterministic value - 0.
Document that behaviour to make it explicit
Reviewed-by: Richard Levitte <levitte@openssl.org>
Reviewed-by: Rich Salz <rsalz@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/4438)
=head1 RETURN VALUES
BN_new() and BN_secure_new()
-return a pointer to the B<BIGNUM>. If the allocation fails,
+return a pointer to the B<BIGNUM> initialised to the value 0.
+If the allocation fails,
they return B<NULL> and set an error code that can be obtained
by L<ERR_get_error(3)>.