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/unity/app_test_unity.cpp

@@ -35,6 +35,7 @@
 #include <test/app/OversizeMeta_test.cpp>
 #include <test/app/Path_test.cpp>
 #include <test/app/PayChan_test.cpp>
+#include <test/app/PayStrand_test.cpp>
 #include <test/app/Regression_test.cpp>
 #include <test/app/SetAuth_test.cpp>
 #include <test/app/SetRegularKey_test.cpp>