Track when we have to abandon the consensus process because the network has moved on.

Issue partial validation if appropriate later.
Change the consensus abort threshold to 80% of trusted nodes. (Maybe there should be a delay?)

src/cpp/ripple/LedgerTiming.h

@@ -66,7 +66,7 @@ public:
 		int previousProposers,		int currentProposers,
 		int currentAgree,			int currentClosed,
 		int previousAgreeTime,		int currentAgreeTime,
-		bool forReal);
+		bool forReal,				bool& failed);
 
 	static int getNextLedgerTimeResolution(int previousResolution, bool previousAgree, int ledgerSeq);
 };