Make `openssl x509 -noout -modulus' functional also for DSA certificates (in

addition to RSA certificates) to match the behaviour of `openssl dsa -noout
-modulus' as it's already the case for `openssl rsa -noout -modulus'.  For RSA
the -modulus is the real "modulus" while for DSA currently the public key is
printed (a decision which was already done by `openssl dsa -modulus' in the
past) which serves a similar purpose.  Additionally the NO_RSA no longer
completely removes the whole -modulus option; it now only avoids using the RSA
stuff. Same applies to NO_DSA now, too.