Make the reachability.c module dirauth-only.

src/core/include.am

@@ -154,7 +154,6 @@ LIBTOR_APP_A_SOURCES = 				\
 # the separation is only in the code location.
 LIBTOR_APP_A_SOURCES += 			\
 	src/feature/dirauth/bwauth.c		\
-	src/feature/dirauth/reachability.c	\
 	src/feature/dirauth/voteflags.c
 
 if BUILD_NT_SERVICES
@@ -179,6 +178,7 @@ MODULE_DIRAUTH_SOURCES = 					\
 	src/feature/dirauth/dsigs_parse.c			\
 	src/feature/dirauth/guardfraction.c			\
 	src/feature/dirauth/process_descs.c			\
+	src/feature/dirauth/reachability.c			\
 	src/feature/dirauth/recommend_pkg.c			\
 	src/feature/dirauth/shared_random.c			\
 	src/feature/dirauth/shared_random_state.c

src/feature/nodelist/routerlist.c

@@ -1926,6 +1926,8 @@ routerlist_remove_old_routers(void)
 void
 routerlist_descriptors_added(smartlist_t *sl, int from_cache)
 {
+  // XXXX use pubsub mechanism here.
+
   tor_assert(sl);
   control_event_descriptors_changed(sl);
   SMARTLIST_FOREACH_BEGIN(sl, routerinfo_t *, ri) {
@@ -1933,7 +1935,9 @@ routerlist_descriptors_added(smartlist_t *sl, int from_cache)
       learned_bridge_descriptor(ri, from_cache);
     if (ri->needs_retest_if_added) {
       ri->needs_retest_if_added = 0;
+#ifdef HAVE_MODULE_DIRAUTH
       dirserv_single_reachability_test(approx_time(), ri);
+#endif
     }
   } SMARTLIST_FOREACH_END(ri);
 }