[vtkusers] Deprecated method for vtkThreshold

[Bill Lorensen]

I have a program that used to work in prior versions of vtk. Now when
I run it, I get the unhelpful message:

vtkThreshold (0x90db1b8): You have set the attribute mode on
vtkThreshold. This method is deprecated, please use
SetInputArrayToProcess instead.

The method I use is:
SetAttributeModeToUseCellData() applied to an instance of vtkThreshold.

It would be nice if the deprecation warning would tell me exactly how
to get this formerly valid program working again.

Thanks,

Bill