test/openssl/test_digest.rb: Add Digest module function to OpenSSL module and test it. Patch provided by Eric Hodel. [ruby-core:46908][Feature #6819] git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@36592 b2dd03c8-39d4-4d8f-98ff-823fe69b080e