[RFC v2 00/19] utrace for 3.0 kernel

[Oleg Nesterov]

Another attempt. This version tries to decouple utrace and ptrace.
This way it is much simpler to follow the upstream changes, afaics.

TODO:

        - The single-stepping updates in ptrace_resume() can race
          with utrace_reset()->user_disable_single_step().

          This was fixed by 20/20, but I noticed that this patch
          is buggy right before sending.

        - Perhaps PTRACE_SYSEMU/TIF_SYSCALL_EMU logic was broken,
          I need to recheck.

        - Testing.

Oleg.