Add info-level log messages during HS-client-state purge

I hope these will never be useful, but having them and not needing them is
better than needing them and not having them.

changes/bug3309

@@ -7,3 +7,7 @@
       refuse to fetch it again for up to 15 minutes.  Bugfix on
       0.2.2.25-alpha; fixes bug 3309.
 
+  o Minor features:
+    - Log (at info level) when purging pieces of hidden-service-client
+      state on SIGNAL NEWNYM.
+

src/or/rendclient.c

@@ -469,6 +469,7 @@ rend_client_purge_last_hid_serv_requests(void)
   last_hid_serv_requests_ = NULL;
 
   if (old_last_hid_serv_requests != NULL) {
+    log_info(LD_REND, "Purging client last-HS-desc-request-time table");
     strmap_free(old_last_hid_serv_requests, _tor_free);
   }
 }

src/or/rendcommon.c

@@ -839,8 +839,10 @@ rend_cache_clean(void)
 void
 rend_cache_purge(void)
 {
-  if (rend_cache)
+  if (rend_cache) {
+    log_info(LD_REND, "Purging client/v0-HS-authority HS descriptor cache");
     strmap_free(rend_cache, _rend_cache_entry_free);
+  }
   rend_cache = strmap_new();
 }