Automatically exhaust response entities returned by ClientResource

[jlouvel]

Currently if the response entity isn't consumed or if exhaust() isn't called explicitly, the connection is blocked.

The idea is to have a default setting that would automatically exhaust() the entity upon release() of the ClientResource. Note that today we only keep track of the latest response, not the history of all calls.

Reported by @stoffeg

[jlouvel]

Consider using the Autoclosable interface http://docs.oracle.com/javase/7/docs/api/java/lang/AutoCloseable.html