Refactor how promise imports are represented in the RPC implementation.
Define Question/Answer/Import/Export nested so we can avoid the silly templates.
Refactor QuestionRef.
Implement handling of Resolve messages.  Though currently they are never sent.
Correctly generate Resolve messages.
Implement handling of 'Release' messages.
Tweaks
Implement embargoes.
unsupportedPipelineOps is not workable.
Oops, don't need to use embargoes if the resolution is on the same machine as the promise, since the network path of calls is unchanged in that case.
Consolidate some redundant code.
Implement exclusive promise joining:  Join two Promise<T>s to create a Promise that resolves when either input resolves.
Tail calls half-implemented, but I think it's time to delete all the cancellation code before continuing because it will simplify things.
Tweaks.
Cancellation isn't evil, just misunderstood.
Finish other end of RPC tail call implementation.
Test and fix promise resolution across RPC.
Test and fix cancellation and release.
Test and fix embargoes.
Don't rely on default assignment operators for cap clients since they break with double virtual inheritance.