bug#25605: [DRAFT PATCH 1/2] Simplify use of FOR_EACH_TAIL

[Eli Zaretskii]

> From: Paul Eggert <eggert@cs.ucla.edu>
> Date: Wed,  1 Feb 2017 15:56:21 -0800
> Cc: Paul Eggert <eggert@cs.ucla.edu>
> 
> * src/data.c (circular_list): New function.
> * src/lisp.h (FOR_EACH_TAIL): Use Brent’s algorithm and C99 for-loop
> decl, to eliminate the need for the args TAIL, TORTOISE and N, and
> to speed things up a bit on typical hosts with optimization.
> All uses changed.

Thanks, but I wonder if you could add some tests for the relevant
functions, I really feel uneasy about changing the implementation of
such basic functionality without any regression tests.