[PATCH] Enable string mempools to work correctly during initialization phase

Hi all,
  this is a subset of my previous memblob-related patch, to make it
more easily auditable.

Extends string mempools so that they can work before the pools
subsystem has been fully initialized, as it happens for instance for
global variables. It does so by explicitly tracking the initialization
state and by expanding early-allocated strings' sizes in order to mark
them as non-pooled.

-- 
    /kinkie