Detect is an incoming "reply" is in fact a pubsub message. If so, do not pop the command queue.

This fixes an issue where the command queue gets popped prematurely by pubsub
messages, leading to callbacks for those commands not being invoked.

Close #360.

Signed-off-by: DTrejo <david.daniel.trejo@gmail.com>
test.js: early return if command not supported