Address some of the comments on CGNR patch

- Rename BlockDiagonalPreconditioner to BlockJacobiPreconditioner
- Include the diagonal in the block jacobi preconditioner.
- Better flag help for eta.
- Enable test for CGNR
- Rename CONJUGATE_GRADIENTS to CGNR.
- etc.
diff --git a/internal/ceres/solver.cc b/internal/ceres/solver.cc
index c45c55f..77f04d1 100644
--- a/internal/ceres/solver.cc
+++ b/internal/ceres/solver.cc
@@ -155,7 +155,7 @@
                           LinearSolverTypeToString(linear_solver_type_given),
                           LinearSolverTypeToString(linear_solver_type_used));
 
-  if (linear_solver_type_given == CONJUGATE_GRADIENTS ||
+  if (linear_solver_type_given == CGNR ||
       linear_solver_type_given == ITERATIVE_SCHUR) {
     internal::StringAppendF(&report, "Preconditioner      %25s%25s\n",
                             PreconditionerTypeToString(preconditioner_type),