* ext/openssl/ossl_config.c: [DOC] Document the following:

  - OpenSSL::ConfigError
  - OpenSSL::Config::DEFAULT_CONFIG_FILE

  Patched by @vbatts via GH-436
  https://github.com/ruby/ruby/pull/436


git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@43667 b2dd03c8-39d4-4d8f-98ff-823fe69b080e