when counting available descs, say whether we're counting exits

src/or/nodelist.c

@@ -1269,8 +1269,9 @@ count_usable_descriptors(int *num_present, int *num_usable,
      }
   SMARTLIST_FOREACH_END(rs);
 
-  log_debug(LD_DIR, "%d usable, %d present (%s).", *num_usable, *num_present,
-            md ? "microdescs" : "descs");
+  log_debug(LD_DIR, "%d usable, %d present (%s%s).",
+            *num_usable, *num_present,
+            md ? "microdesc" : "desc", exit_only ? " exits" : "s");
 }
 
 /** We just fetched a new set of descriptors. Compute how far through