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/Feature.h

@@ -113,7 +113,8 @@ class FeatureCollections
         "HardenedValidations",
         "fixAmendmentMajorityCalc",  // Fix Amendment majority calculation
         "NegativeUNL",
-        "TicketBatch"};
+        "TicketBatch",
+        "FlowSortStrands"};
 
     std::vector<uint256> features;
     boost::container::flat_map<uint256, std::size_t> featureToIndex;
@@ -371,6 +372,7 @@ extern uint256 const featureHardenedValidations;
 extern uint256 const fixAmendmentMajorityCalc;
 extern uint256 const featureNegativeUNL;
 extern uint256 const featureTicketBatch;
+extern uint256 const featureFlowSortStrands;
 
 }  // namespace ripple
 

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.