Fix a case where a node that closed slightly ahead of other ledgers can

think it's out of sync with the network and cause it to jump backwards one
ledger, causing it to be out of sync because the network was about to catch
up to it.

src/cpp/ripple/ValidationCollection.h

@@ -47,7 +47,9 @@ public:
 	int getNodesAfter(const uint256& ledger);
 	int getLoadRatio(bool overLoaded);
 
-	boost::unordered_map<uint256, currentValidationCount> getCurrentValidations(uint256 currentLedger);
+	boost::unordered_map<uint256, currentValidationCount> getCurrentValidations(
+		uint256 currentLedger, uint256 previousLedger);
+
 	std::list<SerializedValidation::pointer> getCurrentTrustedValidations();
 
 	void tune(int size, int age);