Add option to expose full txn across immediate boundary.

[sjudson]

This adds an arity == 2 option for the immediateResponseFunc callback definition, which passes the full transaction object (aka req.oauth2) through across the boundary.

This is an unstructured and generally 'use at your own risk' method, that provides the least ease of use but most power, since the transaction loader may be configured to provide any information through to the decision logic as the implementer sees fit.

[coveralls]

Coverage increased (+0.0009%) to 99.786% when pulling 36ae377 on sjudson:expose-txn into 0516025 on jaredhanson:master.

[jaredhanson]

Merged and released to npm as oauth2orize@1.10.0