Add --core-pattern option to eu-stack

Add --core-pattern option to eu-stack

To backtrace crashed thread from Linux core_pattern handler a special operation
similar to PTRACE_ATTACH needs to be done.  This is implemented as a demo in
eu-stack's core_pattern function invoked by eu-stack's --core-pattern option.

The code of core_pattern function has been suggested by Oleg Nesterov.

src/
2014-11-26  Jan Kratochvil  <jan.kratochvil@redhat.com>

	* stack.c: Include sys/ptrace.h and sys/wait.h.
	(OPT_CORE_PATTERN, opt_core_pattern, core_pattern): New.
	(parse_opt): Handle OPT_CORE_PATTERN.  Check opt_core_pattern option
	validity.  Call core_pattern.  Pass it as assume_ptrace_stopped.
	(main): Add "core-pattern" to options.