Fix method generation in WrappedDistinguishedName.

Without this patch the initializer used downcase to cast the x509 subject entry into a method.
This led to emailAddress being converted to emailaddress, but the classes method is called email_address.
This patch introduces a underscore method that can convert camal-cased entries from x509 subects into
underscore instance methods.
Also added tests for email_address access to DistinguishedName unit tests