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
diff --git a/internal/ceres/levenberg_marquardt_strategy_test.cc b/internal/ceres/levenberg_marquardt_strategy_test.cc
index 370d0a5..8338e5f 100644
--- a/internal/ceres/levenberg_marquardt_strategy_test.cc
+++ b/internal/ceres/levenberg_marquardt_strategy_test.cc
@@ -70,7 +70,9 @@
       EXPECT_NEAR(per_solve_options.D[i], diagonal_[i], kTolerance)
           << i << " " << per_solve_options.D[i] << " " << diagonal_[i];
     }
+    return LinearSolver::Summary();
   }
+
   const int num_cols_;
   const double* diagonal_;
 };