BUG: Fix the weight computation in the InterpolateFunctions method

The InterpolateFunctions method computes the weights using 1/r**2
normalized sum, and Distance2BetweenPoints computes r**2, so the
weight should equal 1.0 / Distance2BetweenPoints.

Change-Id: I73b6d028e67c84ae5a53eddd65a839671e77b564
Merge topic 'FixPolygonInterpolateFunctions' into master

12a9dff6 BUG: Fix the weight computation in the InterpolateFunctions method