Spatial - allow user control of spatial index and recycling per analysis

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What steps will reproduce the problem?
1.  Run a spatial analysis with a condition like '$nbr_y > 3050000'.

What is the expected output? What do you see instead?
All processing groups should have neighbours consisting of all groups north of 
coordinate 3050000.  Instead, the neighbours differ by processing group.  This 
is caused by the spatial index.

The workaround is to turn off the spatial index before running it.

Original issue reported on code.google.com by shawnlaffan on 18 Jan 2011 at 10:37