bug#41440: 26.3; 'replace' argument in function 'shell-command-on-region' is assumed to be always t for rectangle selection

[Eli Zaretskii]

> From: Warren Lynn <wrn.lynn@gmail.com>
> Date: Thu, 21 May 2020 14:53:05 -0400
> 
> I am gladly surprised to find out function
> shell-command-on-region
> is supposed to work on rectangle selection also (with 
> 'region-noncontiguous-p' set to t), but then
> disappointed to find out the feature does not work. It has two problems:
> 
> 1. As this email title says, argument 'replace' is assumed to be t no matter 
> what.
> 2. Even if I really want to replace the original selection with the 
> shell-command output, it still does not work.
> An error will be thrown in function "cua--insert-rectangle" due to some 
> argument type mismatch.
> 
> This feature will be very useful to me (and hopefully others too) and I hope 
> somebody can fix the above.

Juri, could you please look into this?  In addition to the problem
described in the bug report, the 'region-noncontiguous-p' argument is
not mentioned in the doc string and not in the manual.  I'd like to
fix that for Emacs 27, please.

Thanks.