[Dbix-class] Live object index support ported

[Marcus Ramberg]

Matt S Trout skrev:

> We definitely need an implementation, because there're a fair number of
>
>people out there whose code needs it, and when it's useful it's *very*
>useful. But it's not core, and while it has to be loaded for "full compat
>mode"[1], we may want two (three?) default recipes - one with LiveObjectIndex,
>one with FastMmapIndex, and maybe one with MemcachedIndex or something else
>cross-machine-ish.
>  
>
I think a memory cached version of some sort is really the way to go. 
The live object index version can probably just be a wrapper around it. 
The most important thing is that it will work out of the box, so people 
won't be forced to do a lot of hassle to set up the live object index. I 
guess providing alternatives is good, but the core should probably just 
support one method, to keep it lightweight?

Marcus