Bring back default redirect for profiling.

Now that the RPC server uses its own mux, bring back the code which does
the automatic 303 redirect for the root of the profile server.

btcd.go

@@ -48,6 +48,9 @@ func btcdMain() error {
 		go func() {
 			listenAddr := net.JoinHostPort("", cfg.Profile)
 			log.Infof("Profile server listening on %s", listenAddr)
+			profileRedirect := http.RedirectHandler("/debug/pprof",
+				http.StatusSeeOther)
+			http.Handle("/", profileRedirect)
 			log.Errorf("%v", http.ListenAndServe(listenAddr, nil))
 		}()
 	}