bug#12085: 24.1; doc string of `regexp-opt-charset'

[Drew Adams]

First, it is unfortunate that this function uses the term "charset" in
its name, where it really means a list of characters and not an Emacs
character set, which is what we normally mean by "charset".
 
At least the Elisp manual doc for the function makes it clear that the
argument is a list of characters (and not, for example, a charset).
 
But the doc string does not make that clear.  It says nothing at all
about CHARS.  CHARS could be an integer or a hash table or a vector, for
all we know from the doc string.
 
That's the bug: state that CHARS is a list of characters.
 
And perhaps think about renaming this function to `regexp-opt-charlist',
or just `regexp-opt-chars'.

In GNU Emacs 24.1.1 (i386-mingw-nt5.1.2600)
 of 2012-06-10 on MARVIN
Windowing system distributor `Microsoft Corp.', version 5.1.2600
Configured using:
 `configure --with-gcc (4.6) --cflags
 -ID:/devel/emacs/libs/libXpm-3.5.8/include
 -ID:/devel/emacs/libs/libXpm-3.5.8/src
 -ID:/devel/emacs/libs/libpng-dev_1.4.3-1/include
 -ID:/devel/emacs/libs/zlib-dev_1.2.5-2/include
 -ID:/devel/emacs/libs/giflib-4.1.4-1/include
 -ID:/devel/emacs/libs/jpeg-6b-4/include
 -ID:/devel/emacs/libs/tiff-3.8.2-1/include
 -ID:/devel/emacs/libs/gnutls-3.0.9/include'