[xml] Remove an xml file's dependence on external DTD files

[职文超 <venture g gmail com>]

I am new to XML. And I am looking for a way to convert an xml file
depending on external DTD files to its equivalent not depending on
external DTD files.

I want to do this because I want to parse an xml file with VTD-XML
parser. But the VTD-XML parser doesn't support DTD. So when a xml file
references entities defined in external DTD files, VTD-XML will fail to
parse it.

Any suggestion will be appreciated.