Changed pointreg to use new SampleShift, LineShift, and PixelShift...

Changed pointreg to use new SampleShift, LineShift, and PixelShift functionality in ControlMeasure in reference to issue #159.  Incidentally, also fixes a bug where SampleShift and LineShift were reported incorrectly as being ORIGINAL_MEASUREMENT - NEW_MEASUREMENT, which of course is the negation of the correct output: NEW_MEASUREMENT - ORIGINAL_MEASUREMENT.

git-svn-id: http://subversion.wr.usgs.gov/repos/prog/isis3/trunk@2808 41f8697f-d340-4b68-9986-7bafba869bb8