Ticket 49028 - Autosize database cache by default.
    
    Bug Description:  We ship Directory Server with very conservative defaults.
    These are often not fit for production, yet many people run with them and
    complain about the performance of Directory Server.
    
    Fix Description:  Instead of relying on the admin to tune their system, by
    defaulting to the autotuning newly installed systems will get the "best possible"
    experience. Please see:
    
    http://www.port389.org/docs/389ds/design/autotuning.html
    
    Additionally, we now clamp autotuned caches to 64mb boundaries, and default to
    cachesizes of 0. If we detect 0, we run the autotune, if else we leave it alone.
    This way existing installs won't see a change, but new deployments will
    autoscale to the hardware. Existing users of autosizing who want the value to
    change every startup will still have the same behaviour.
    
    https://fedorahosted.org/389/ticket/49028
    
    Author: wibrown
    
    Review by: nhosoi (Thanks!)