New rules for payment paths:

* Sanity check on newly created strands
* Better loop detection
* Better tests (test every combination of path element pairs)
* Disallow any root issuer (even for xrp)
* Disallow compount element typs in path
* Issue was not reset when currency was XRP
* Add amendment

src/test/app/SetAuth_test.cpp

@@ -46,13 +46,13 @@ struct SetAuth_test : public beast::unit_test::suite
         return jv;
     }
 
-    void testAuth()
+    void testAuth(std::initializer_list<uint256> fs)
     {
         using namespace jtx;
         auto const gw = Account("gw");
         auto const USD = gw["USD"];
         {
-            Env env(*this);
+            Env env(*this, features(fs));
             env.fund(XRP(100000), "alice", gw);
             env(fset(gw, asfRequireAuth));
             env(auth(gw, "alice", "USD"),       ter(tecNO_LINE_REDUNDANT));
@@ -75,7 +75,9 @@ struct SetAuth_test : public beast::unit_test::suite
 
     void run() override
     {
-        testAuth();
+        testAuth({});
+        testAuth({featureFlow});
+        testAuth({featureFlow, featureToStrandV2});
     }
 };