wishlist item: add version support info to doc strings

[era eriksson]

In GNU Emacs 19.34.1 (alpha-dec-osf4.0, X toolkit) of Wed Mar  5 1997 on kantti

Please describe exactly what actions triggered the bug
and the precise symptoms of the bug:

As someone who still occasionally has to work on systems where
administration refuses to take the plunge and move to Emacs v20, I
would very much appreciate it if new Lisp functions could be annotated
with a remark about in which version of Emacs they were introduced.
Presently, writing Elisp code which works on Emacs 19 and Emacs 20 is
very much a matter of trial and error, at least when Emacs 20 is your
primary platform.

As an example, I just happened to stumble over a useful function
`substitute-key-definition' which I wasn't aware of before. But before
I can use it for anything, I have to connect to the system where I'm
still stuck with Emacs 19, and fire up Emacs and look for this
function in this version of Emacs. (Turns out it's supported. Good
good.)

As another example, some Common Lisp idioms are available in v19, but
only with (require 'cl). Since I use packages which require cl, I end
up with the impression that those functions are supported (although in
many cases, C-h f <function> will indicate this potential portability
problem with something like "<function>: a Lisp macro in  cl'." But
even this is problematic because then you have to figure out what to
do when cl on Emacs 20 does not provide the macro in question. [Not
sure if this is an issue really.])

I do realize that adding this information retroactively can be a huge
hassle, but perhaps at least you could consider adopting this as a
documentation convention from now on when adding new functions.


I've taken the liberty to trim the "Recent input" and "Recent messages" 
dumps from here, as they are hardly relevant.

/* era */

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