Implement probe_lua and add it to lpxclient/lpxserver

luprex/core/cpp/world.hpp

@@ -166,6 +166,15 @@ public:
     //
     Redirects fetch_redirects();
 
+    // Probe an arbitrary lua expression.
+    //
+    // Any print-statements in the lua code are sent into
+    // a stringstream.  The return value of probe_lua is the string
+    // from the stringstream.  If the lua expression returns a
+    // value, that is also printed to the stringstream.
+    //
+    std::string probe_lua(int64_t actor_id, const std::string &lua);
+
     // Probe the 'interface' function of the specified sprite.
     //
     void update_gui(int64_t actor_id, int64_t place_id, Gui *gui);