Locking: Add contin tracing to detect deadlocks

We added the code to trace all the contins linked to a particular
Lockvoker, into SerializedAsyncContinuation. This basically
ensures that we'll almost never deal with a deadlock. So cool.

include/asynchronousContinuationChainLink.h

@@ -18,6 +18,9 @@ class AsynchronousContinuationChainLink
 {
 public:
     virtual ~AsynchronousContinuationChainLink() = default;
+
+	virtual std::shared_ptr<AsynchronousContinuationChainLink>
+	getCallersContinuation() = 0;
 };
 
 } // namespace smo