[PATCH, doc RFA][PR 15276] Add $_caller_is, et. al.

[Eli Zaretskii]

> From: Doug Evans <xdje42@gmail.com>
> Date: Mon, 01 Sep 2014 16:07:01 -0700
> 
> Redhat has $caller_is and $caller_matches in their tree.
> I've had a use for them from time to time, and I've finally gone ahead
> and finished the patch so that it can be submitted.
> 
> I've also had a use for $_any_caller_is/$_any_caller_matches so I've
> added those too.

OK for the documentation parts.

Thanks.