OrderedGroups implementation.

This generalizes the Ordering object and paves the path for a more
general inner iteration API.

Change-Id: I6efce5f999c2bfab5f90a8a18e21140581f207cd
diff --git a/internal/ceres/CMakeLists.txt b/internal/ceres/CMakeLists.txt
index e094f6a..e0e8afa 100644
--- a/internal/ceres/CMakeLists.txt
+++ b/internal/ceres/CMakeLists.txt
@@ -235,6 +235,7 @@
   CERES_TEST(normal_prior)
   CERES_TEST(numeric_diff_cost_function)
   CERES_TEST(ordering)
+  CERES_TEST(ordered_groups)
   CERES_TEST(parameter_block)
   CERES_TEST(partitioned_matrix_view)
   CERES_TEST(polynomial_solver)