bug#25618: 25.1.91; More precise limit for tagging expensive tests

[Eli Zaretskii]

> From: Tino Calancha <tino.calancha@gmail.com>
> Date: Sat, 04 Feb 2017 22:42:44 +0900
> 
> 
> Prefer set a numeric limit of seconds than using the word 'few'.
> 
> For instance, in my box the test `cl-seq-test-bug24264' in
> test/lisp/emacs-lisp/cl-seq-tests.el
> takes 7 s.
> With an explicit numeric threshold is easier to decide whether this test
> must be tagged as expensive or not.
> 
> In following patch i define a few as 2-3 seconds.  Other people might
> prefer 4-5 or even higher.
> Please, suggest a proper value to consider a test as expensive.

I think 2-3 sec is negligible, and 7 sec is not long enough to annoy.
10 sec or more is beginning to sound like it comes close to "too
long", and 20 sec is definitely too long.