* Fixed handling of ASYN messages, I think.

  - If no callback has been registered for a particular command, the _CxClRecv()
  command will actively skip all of the ASYN message (not sure if this works
  correctly for _all_ messages... will wait and see)
* Fixed delivery of express messages.  Misunderstood protocol.
! Need to detect server capabilities and use old-style SEXP when necessary!  At
  present, libCxClient is incompatible with older servers.  This, I assume, is a
  bad thing.