XML signature wrapping attack

ruby-saml prior to version 1.3.0 is vulnerable to an XML signature wrapping attack
in the specific scenario where there was a signature that referenced at the same time
2 elements (but past the scheme validator process since 1 of the element was inside
the encrypted assertion).

ruby-saml users must update to 1.3.0, which implements 3 extra validations to
mitigate this kind of attack.