[Catalyst] C::P::PageCache patch for reducing duplicate processing

[Perrin Harkins]

Toby Corkindale wrote:
> One of the aims of my patch is to avoid the expense of having numerous 
> processes produce the same code simultaneously. So on the initial bunch 
> of requests, I'll still try and have the code delay all-but-one of them 
> from building the page.

Presumably this only happens when a new cached page suddenly becomes 
available and is instantly in high demand.  It's not very frequent.  In 
my opinion, that isn't worth the danger of messing with something as 
potentially troublesome as locks that block page generation, but I 
suppose no one is forced to use the locking.

- Perrin