Closes#797Closes#798
JAXRSContract sets a single Content-Type value
This change allows headers to be cleared by passing a null
value for backwards compatibility.
Multiple Content-Type values are not valid because the body
that we send with any given request will only have a single
type.
Updated header entry assertion to be agnostic to header name
order.
* RequestTemplate.headers clear behavior matches that of query params
Carter Kozak
Dan Goslen
adriancole