Update config for v2.6 compatability

In version 2.6, directives relating to virtual memory have been removed and directives relating to hash-max-zipmap have been renamed to hash-max-ziplist.

This change maintains the current v2.4 configuration, but includes updates to: add a flag to disable vm directives; make the hash-max-zipmap directives configurable via attributes and add a flag to disable them; and add directives for hash-max-ziplist that are configurable via attributes and add a flag to enable them.

I've verified the updated config works with v2.6 on Ubuntu Server 12.04 AMD64.