Fix memory errors (#108)

* frees getUint64Tuple tuple iterator

* explicitly create strand in synchronous()

src/backend/BackendInterface.cpp

@@ -252,8 +252,9 @@ BackendInterface::fetchLedgerPage(
     std::vector<ripple::uint256> keys;
     while (keys.size() < limit)
     {
-        ripple::uint256 const& curCursor =
-            keys.size() ? keys.back() : cursor ? *cursor : firstKey;
+        ripple::uint256 const& curCursor = keys.size() ? keys.back()
+            : cursor                                   ? *cursor
+                                                       : firstKey;
         auto succ = fetchSuccessorKey(curCursor, ledgerSequence, yield);
 
         if (!succ)