Add Problem::GetParameterization.

This allows the user to query the local parameterization associated
with a parameter block.

Change-Id: I3ab274aa88221c8e2def7c463825bf3927b1fdc9
diff --git a/internal/ceres/problem_impl.h b/internal/ceres/problem_impl.h
index 35c16cd..da50578 100644
--- a/internal/ceres/problem_impl.h
+++ b/internal/ceres/problem_impl.h
@@ -127,6 +127,7 @@
   void SetParameterBlockVariable(double* values);
   void SetParameterization(double* values,
                            LocalParameterization* local_parameterization);
+  const LocalParameterization* GetParameterization(double* values) const;
 
   bool Evaluate(const Problem::EvaluateOptions& options,
                 double* cost,