lib/dom: allow `xml` in tag name
lib/dom: allow `xml` in tag name

I'm not sure, what was the reason of this, security concerns maybe?
In this case I can change it as an option.

But we want this parser to parse correctly formed XML documents.

Signed-off-by: Alexandre Terrasa <b30f4169e054ee7b8c243480bcfcef62416f3b08@moz-code.org>

privat/nit,privat/nit,privat/nit,privat/nit,privat/nit,privat/nit,privat/nit,privat/nit,privat/nit,privat/nit