[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.