Overhaul of thread handling to support blocking functions other than wait

luprex/core/cpp/traceback.hpp

@@ -22,9 +22,11 @@ int traceback_coroutine(lua_State *L);
 
 // traceback_pcall
 //
-// same as lua_pcall, except that it automatically supplies 
-// traceback_coroutine as a message handler.
+// Similar to lua_pcall, except that it automatically supplies 
+// traceback_coroutine as a message handler.  It also automatically
+// returns any error message.  Returns empty string if there's
+// no error.
 //
-int traceback_pcall(lua_State *L, int narg, int nret);
+eng::string traceback_pcall(lua_State *L, int narg, int nret);
 
 #endif // TRACEBACK_HPP