> I'd like to clarify the specification. Should the following code show true? or false?
>
> Signal.trap(:USR1) do
>   Process.kill(:USR2, $$)
> end
> Signal.trap(:USR2) do
>   p Process.in_trap?(:USR2)   # => true
>   p Process.in_trap?(:USR1)   # => true or false?
> end
> Process.kill(:USR1, $$)
> sleep

false.

Because trap handler never be nested. I changed it at 2.0 for
preventing stack overflow issue.
No confusion.