* test/openssl/test_x509_cert.rb: Perform SHA-256 tests only if
supported by the available OpenSSL version. Versions < 0.9.8 don't
support it. [ruby-core:37724]
git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@32366 b2dd03c8-39d4-4d8f-98ff-823fe69b080e