Hi,

I am using Emacs 23.2.1. I think sgml-xml-auto-coding-function() should
respect the *-with-signature-* coding.

Consider the scenario below:
1. xml file with the signature \376\377 at beginning of the file and the
first line is
<?xml version="1.0" encoding="utf-16be"?>
2. edit this file and save it. sgml-xml-auto-coding-function will use the
utf-16be to save the file.
3. open the file again, get messed.

In this case sgml-xml-auto-coding-function() shouldn't change the coding and
if it really need to change the coding, it should append the
*-with-signature-* to the selected coding.

sgml-html-meta-auto-coding-function() should have same problem.