Various fixes repored by Markus Moll.

1. Termination type was using == instead of =.
2. LevenbergMarquardtStrategyTest was using an object
   which was not returning the correct value.
3. DumpLinearLeastSquaresProblemToTextFile was passing an
   unnecessary argument to StringAppendF.

Change-Id: Ie7598c8e3d504763c889737a0d5cec805d52bbaf