Down-integrate some code from an internal branch.  (More to come.)

diff --git a/examples/add_person.cc b/examples/add_person.cc
index 2aca216..b9ca44f 100644
--- a/examples/add_person.cc
+++ b/examples/add_person.cc
@@ -88,5 +88,8 @@
     }
   }
 
+  // Optional:  Delete all global objects allocated by libprotobuf.
+  google::protobuf::ShutdownProtobufLibrary();
+
   return 0;
 }
diff --git a/examples/list_people.cc b/examples/list_people.cc
index bd9a583..5363152 100644
--- a/examples/list_people.cc
+++ b/examples/list_people.cc
@@ -61,5 +61,8 @@
 
   ListPeople(address_book);
 
+  // Optional:  Delete all global objects allocated by libprotobuf.
+  google::protobuf::ShutdownProtobufLibrary();
+
   return 0;
 }