set sgml-xml-mode to true in some modes derived from sgml-mode

[Yilkal Argaw <yilkalargawworkneh@gmail.com>]

Hi All

While trying to use emacs to edit html files I noticed how the
sgml-tag functions which uses skeletons to insert  tags does not
insert a closing tag for some tags like "<li>" this behaviour changes
by changing the variable "sgml-xml-mode" to a non nil value. Would it
not be better to turn this variable to true some of the derived modes
like html-mode and xml-mode. This can be done by setting the variable
in the autoload section for the derived modes.  This makes the default
behaviour of those modes more usable without using hooks. For now I am
using hooks set the variable true for html, mhtml and xml modes but I
think that it should be set by default for it to be more user
friendly.

With Regards
Yilkal