Add 'getValidatedLedger' to get the last fully-validated ledger.

We should probably audit calls to 'getClosedLedger' to see if they should use this instead.

src/cpp/ripple/LedgerMaster.h

@@ -72,6 +72,9 @@ public:
 	// The finalized ledger is the last closed/accepted ledger
 	Ledger::ref getClosedLedger()		{ return mFinalizedLedger; }
 
+	// The published ledger is the last fully validated ledger
+	Ledger::ref getValidatedLedger()	{ return mPubLedger; }
+
 	TER doTransaction(const SerializedTransaction& txn, TransactionEngineParams params);
 
 	void pushLedger(Ledger::ref newLedger);