Infinite Recursion During Coercion of Encrypted Responses

[dbrrr]

Encrypted response, unlike normal responses, are: org.opensaml.xmlsec.encryption.impl.EncryptedDataImpl. This causes an infinite loop when coercing to a Response, because it's never coerced to an Element. I believe we may need to decrypt first before we can get a org.opensaml.core.xml.XMLObject and have the rest of the coercions work.

We need to figure out a graceful way to handle this: the rest of the code expects a Response pretty early in the process, so either we need to identify/decrypt encrypted responses before handing them to the rest of the verification code, or have the caller do it.

Test case added in #47