Change to cast in inker/iclerk interaction

This allows for leveled_iclerk:clerk_stop to be a sync call, so that files will only be closed once the iclerk has stopped.  This is designed ot prevent iclerk crashes during shutdowns when files it is depnding on are closed mid shutdown.

test/end_to_end/tictac_SUITE.erl

@@ -724,6 +724,9 @@ basic_headonly_test(ObjectCount, RemoveCount, HeadOnly) ->
     
     {ok, FinalFNs} = file:list_dir(JFP),
 
+    ok = leveled_bookie:book_trimjournal(Bookie1),
+    % CCheck a second trim is still OK
+
     [{add, SegmentID0, Bucket0, Key0, Hash0}|_Rest] = ObjectSpecL,
     case HeadOnly of 
         with_lookup ->