[vtkusers] Compile time checking and new pipeline

[Mathieu Malaterre]

> Could a bit more flavour be given to vtkAlgorithmOutput to trap this 
> kind of error?

Hi John,

	Are you redirecting the vtkWindowOuput to a file or something ? You 
should get an error that looks like:

ERROR: In vtkDemandDrivenPipeline.cxx, line 777
vtkStreamingDemandDrivenPipeline (0x822fc00): Input for connection index 
0 on input port index 0 for algorithm 
vtkPainterPolyDataMapper(0x822f6b0) is of type vtkUnstructuredGrid, but 
a vtkPolyData is required.


Mathieu