bug#13052: 24.3.50; mention recent change of `kbd' to a function in NEWS

[Drew Adams]

> > Why?  What makes it special?
> 
> Do you really think that there are many things in byte-opt.el intended
> for third-party packages? The only reference to it in the docs is in
> Writing Emacs Primitives, which is not exactly lisp-level stuff.

The application of property `pure' to `kbd' is not in byte-opt.el.  It is in
subr.el.  And in my code it would, likewise, be in an ordinary Lisp library.

I was just asking whether you know of something that makes this special to Emacs
Dev and not appropriate for user libraries.  If you don't know of anything,
fine; perhaps someone else does.

It is a question: whether `pure' is information that users can reasonably use to
inform the byte compiler that a function is what the compiler would expect of a
pure function, i.e., what the code you pointed me to would expect, in order to
be able to perform that particular optimization.