bug#7491: Support for DocBook .dbk extension

[Chong Yidong]

Rob Browning <rlb@defaultvalue.org> writes:

>> A common file extension for DocBook files is '.dbk', which is not
>> commonly used for any other purpose, at least on Linux.
>
> Though I'm not familiar with the extension myself, I noticed that the
> Wikipedia DocBook entry (http://en.wikipedia.org/wiki/DocBook) also
> mentions it.  Would it be appropriate to add support, presumably via
> auto-mode-alist and schemas.xml?
>
> The original report,
> http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=498125, contains a
> patch against the Debian nxml-mode package.  It would need some
> adjustment to work with Emacs itself.

Fixed, thanks.