alist-get in Emacs 24?

[Marcin Borkowski <mbork@mbork.pl>]

Hi all,

some time ago, someone here recommended the alist-get function to me.
It works like a charm for me, but not for some other user who's running
Emacs 24.

While writing (or copying from subr.el) an alist-get "getter" version is
trivial, the "setter" version (which I need for setf, cl-incf and
cl-decf) is a bit harder for me.  Looking at

(gv-define-expander alist-get ...)

in gv.el makes my head explode.  I will probably just write functions
like set-alist-element and inc-alist-element (or maybe I'll name them
better) so that the library works in Emacs 24, but is there a better
way?  (Note: while I'm fairly confident that I could understand that
gv-define-expander stuff, it would probably take a lot of time.  This is
the long-term plan.  Now my goal is to help that user ASAP.)

Also, what would be the recommended policy for supporting older Emacsen?
Is it enough to test my packages against 24.1 (which didn't compile on
my machine anyway, btw)?  Should I care for Emacs 23 at all?

TIA,

-- 
Marcin Borkowski
http://octd.wmi.amu.edu.pl/en/Marcin_Borkowski
Faculty of Mathematics and Computer Science
Adam Mickiewicz University