[CRIU] Rework open_proc() and friends

[Kir Kolyshkin]

On 02/17/2012 01:39 AM, Kir Kolyshkin wrote:
> This epic series tries to simplify the way we work with /proc/PID files,
> and it tries to do that gradually. That essentially means that if you
> do not like the last patch, you can still enjoy the first four.
>
> DISCLAIMER: while the code looks correct, it has only been
> tested by gcc and my eyes; i.e. I haven't run it.

OK thanks to Cyrill I ran 'make test' with and without these patches -- 
no regressions
(got 68 PASS lines in both cases).