Optimize payment path exploration in flow:

* Use theoretical quality to order the strands
* Do not use strands below the user specified quality limit
* Stop exploring strands (at the current quality iteration) once any strand is non-dry

src/ripple/protocol/impl/Feature.cpp

@@ -133,6 +133,7 @@ detail::supportedAmendments()
         "fixAmendmentMajorityCalc",
         //"NegativeUNL",      // Commented out to prevent automatic enablement
         "TicketBatch",
+        "FlowSortStrands",
     };
     return supported;
 }
@@ -186,7 +187,8 @@ uint256 const
     featureHardenedValidations      = *getRegisteredFeature("HardenedValidations"),
     fixAmendmentMajorityCalc        = *getRegisteredFeature("fixAmendmentMajorityCalc"),
     featureNegativeUNL              = *getRegisteredFeature("NegativeUNL"),
-    featureTicketBatch              = *getRegisteredFeature("TicketBatch");
+    featureTicketBatch              = *getRegisteredFeature("TicketBatch"),
+    featureFlowSortStrands          = *getRegisteredFeature("FlowSortStrands");
 
 // The following amendments have been active for at least two years. Their
 // pre-amendment code has been removed and the identifiers are deprecated.