Provides a per-container statistics concerning the numbers of tasks
in various states, system and user times, etc. Patch is inspired
by Paul's example of the used CPU time accounting. Although this
patch is independent from Paul's example to make it possible playing
with them separately.

Based on Paul Menage containers v8.

One thing left is the idle time accounting. The problem in idle
time accounting is that the algorithm used to calculate global idle
time is useless. When system is loaded with tasks (and thus have
0% idle) some containers may be idle, i.e. no tasks run within a
container.

A known feature of this patch is that the numbers of tasks
shown for top container are not 100% true, as by the time the
top container is created system is already running. Probably
this statistics is simply not needed for top container.