Big scary change

[Ken Martin]

I just checked in some significant changes to the data objects. The basic 
problem was that after the imaging and graphic pipelines were merged, the 
imaging pipeline was always reallocating data each update even when the old 
scalar array was the right size for the new data. This was not the case in 
vtk2.4 etc. I have put in changes that I think fix this problem and do not 
introduce other problems (we will see). I ran a bunch ( > 100) of 
regression tests and they worked but there may be other problems.

- Ken