Dogleg strategy and timing cleanups.

1. A new dogleg trust region strategy.
2. Consistent naming of all variables taking and reporting
   time. Also all are doubles now.
3. Enum to stringification routines.
4. bundle_adjuster.cc accepts max solver time and trust_region_strategy.
5. Time accounting is pushed into solver_impl.cc and there is now
   postprocessing time accounted for explicitly.
6. IterationCallback now has cumulative time.
7. LoggingCallback logs per iteration and cumulative time.
8. TrustRegionStrategy now allows for Invalid steps to be indicated
   explicitly.
9. Trust region minimizer actually terminates on max_solver_time.

Change-Id: I7e3b82c8beebc17b6b355ea46ddd280754a2d8b2
diff --git a/internal/ceres/types.cc b/internal/ceres/types.cc
index c6c4dea..18fefad 100644
--- a/internal/ceres/types.cc
+++ b/internal/ceres/types.cc
@@ -97,6 +97,26 @@
   }
 }
 
+const char* SparseLinearAlgebraTypeToString(
+    SparseLinearAlgebraLibraryType sparse_linear_algebra_library_type) {
+  switch (sparse_linear_algebra_library_type) {
+    CASESTR(CX_SPARSE);
+    CASESTR(SUITE_SPARSE);
+    default:
+      return "UNKNOWN";
+  }
+}
+
+const char* TrustRegionStrategyTypeToString(
+    TrustRegionStrategyType trust_region_strategy_type) {
+  switch (trust_region_strategy_type) {
+    CASESTR(LEVENBERG_MARQUARDT);
+    CASESTR(DOGLEG);
+    default:
+      return "UNKNOWN";
+  }
+}
+
 #undef CASESTR
 
 bool IsSchurType(LinearSolverType type) {