Add config option to disable the localhost workaround

There are some network configurations in which it's undesirable; such as
reverse tunneling through ssh. These are obscure enough to allow leaving
the option undocumented (in the example config file).

src/settings.hpp

@@ -7,6 +7,7 @@ namespace settings {
     extern int DBSAVEINTERVAL;
     extern int SHARDPORT;
     extern std::string SHARDSERVERIP;
+    extern bool LOCALHOSTWORKAROUND;
     extern time_t TIMEOUT;
     extern int VIEWDISTANCE;
     extern bool SIMULATEMOBS;