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

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

A problem with replication with multiple slaves connectiong to a single master fixed. It was due to a typo, and reported on github by the user micmac. Also the copyright year fixed from many files.

SPOP implemented. Hash table resizing for Sets and Expires too. Changed the resize policy to play better with RANDOMKEY and SPOP.