issue #223: correctly detect if reversible data have to be removed after hived restart

• now fork event is added only when hived wills end notification, no artificial event during 'hive.connect'
• hive.connect is always executed before on_reindex notification, before data are marked as dirty

src/hive_fork_manager/hived_api.sql

@@ -27,10 +27,6 @@ $BODY$
 DECLARE
     __fork_id BIGINT;
 BEGIN
-    IF (SELECT COUNT(*) FROM hive.fork ) > 0 THEN
-        RETURN;
-    END IF;
-
     INSERT INTO hive.fork(block_num, time_of_fork)
     VALUES( _block_num_before_fork, LOCALTIMESTAMP );