make sure that cmpobj is in decoded form when sorting by ALPHA (this solves edge case from previous commit where (!sortby && alpha) == 1)

set refcount of string objects retrieved from zipmaps to 0, so we don't have to touch the refcount of the objects inside dicts

Incrementally rehahsing hash table! Thanks to Derek Collison and Pieter Noordhuis for feedbacks/help

Now all the commands returning a multi bulk reply against non existing keys will return an empty multi bulk, not a nil one

use directly the real key object in VM I/O jobs to match by pointer, and to handle different keys with the same name living in different DBs, but being at the same moment in the IO job queues

Prevent hash table resize while there are active child processes in order to play well with copy on write