1) I added an example that uses a plot plugin. It opens a file, loads the 
   pseudocolor plot, loads the clip operator, creates a pseudocolor plot, 
   applies the clip operator, adds the plot to a vis window, renders an 
   image and saves the image.

2) I did some minor code cleanup to a couple of the avt examples.

3) I modified the pseoducolor plot so that it initializes a look up table
   when setting the color table so that the newly added example would work.



git-svn-id: http://visit.ilight.com/svn/visit/trunk/src@25293 18c085ea-50e0-402c-830e-de6fd14e8384