descriptor statements have the following shortcomings

- input descriptors (USING DESCRIPTOR <name>) are not supported
  
  Reason: to fully support dynamic SQL the frontend/backend communication
  	should change to recognize input parameters.
  	Since this is not likely to happen in the near future and you
  	can cover the same functionality with the existing infrastructure
  	(using s[n]printf), I'll leave the work to someone else.

