free hash table entries about no longer active classes, so that PUBSUB can be abused with millions of different classes

Fixed a critical replication bug: binary values issued with the multi bulk protocol caused a protocol desync with slaves.

Fixed the reply about denied  write commands under maxmemory reached condition: now the error will no longer lead to a client-server protocol desync

the Cron timer function is now called 10 times per second instead of 1 time per second to make Redis more responsibe to BGSAVE and to delete expired keys more incrementally