THRIFT-727 - C++: what() method of generated exceptions will provide more information

Patch: Anna Dymek <aadymek@gmail.com>
Client: C++

This closes #469
diff --git a/tutorial/cpp/CppClient.cpp b/tutorial/cpp/CppClient.cpp
index 258cbd6..2763fee 100644
--- a/tutorial/cpp/CppClient.cpp
+++ b/tutorial/cpp/CppClient.cpp
@@ -58,6 +58,7 @@
     } catch (InvalidOperation& io) {
       cout << "InvalidOperation: " << io.why << endl;
       // or using generated operator<<: cout << io << endl;
+      // or by using std::exception native method what(): cout << io.what() << endl;
     }
 
     work.op = Operation::SUBTRACT;