Use structured bindings in some places:

Most of the new uses either:
* Replace some uses of `tie`
* bind to pairs when iterating through maps

src/test/csf/Digraph.h

@@ -226,10 +226,10 @@ public:
     saveDot(std::ostream & out, VertexName&& vertexName) const
     {
         out << "digraph {\n";
-        for (auto const& vData : graph_)
+        for (auto const& [vertex, links] : graph_)
         {
-            auto const fromName = vertexName(vData.first);
-            for (auto const& eData : vData.second)
+            auto const fromName = vertexName(vertex);
+            for (auto const& eData : links)
             {
                 auto const toName = vertexName(eData.first);
                 out << fromName << " -> " << toName << ";\n";

src/test/csf/Histogram.h

@@ -91,9 +91,9 @@ public:
             return tmp;
         // Since counts are sorted, shouldn't need to worry much about numerical
         // error
-        for (auto const& it : counts_)
+        for (auto const& [bin, count] : counts_)
         {
-            tmp += it.first * it.second;
+            tmp += bin * count;
         }
         return tmp/samples;
     }

src/test/csf/Peer.h

@@ -801,11 +801,11 @@ struct Peer
     bool
     handle(TxSet const& txs)
     {
-        auto const it = txSets.insert(std::make_pair(txs.id(), txs));
-        if (it.second)
+        bool const inserted = txSets.insert(std::make_pair(txs.id(), txs)).second;
+        if (inserted)
             consensus.gotTxSet(now(), txs);
         // relay only if new
-        return it.second;
+        return inserted;
     }
 
     bool