[EJBCLIENT-170] Do not propagate transactions for async methods unless forced to

[dmlloyd]

The policy is:

• If there is a ClientTransaction annotation on the method, use the specified mode, otherwise:
• If the method is asynchronous (returns Future or is tagged with the ClientAsynchronous annotation), use NOT_SUPPORTED, otherwise:
• If the method's enclosing class has a ClientTransaction annotation, use the specified mode, otherwise:
• Use the default mode (SUPPORTS).

[dmlloyd]

A key weakness of this approach is that it does not account for one-way (void-returning) asynchronous methods. Those will generally be handled on the server anyway. But we don't have a way on the server to force inflow of a transaction, nor do we want one for void methods: we can never know when the method completes, therefore we can never know when it's safe to complete the transaction.

I'm thinking that the server policy will be to always ignore the transaction for void async, if it comes in, and the client would know this happened because of the proceed-async message. For Future-returning async methods, if the transaction is present (and the client is new), the server should inflow it (because it means the user must have specifically opted in to it). If the client is old, then the server probably should ignore it in the same way as done for void-returning methods.