JavaDocs for Client, WebTarget and Invocation should clearly say whether invocations MUST be thread-safe

JAX-RS 2.0 provides a Client API which is prepared for intense reuse of object instances of Client, WebTarget and Invocation. Unfortunately the JavaDocs of these classes do not say whether a caller can rely upon these instances are thread-safe. As a recent discussion on the user's mailing list has discovered, users abstain from the rist of concurrent usage of these instances as they fear risk of producing problems. Hence, the JAX-RS 2.1 specification should clearly point out (in PDF and / or JavaDocs) whether implementations of Client, WebTarget and Invocation MUST be thread-safe. This unambiguity would allow users to safely the same Client instance from different application threads for example.
#### Affected Versions
[2.1]