For tests that loaded the same document twice (typically for WRONG_DOCUMENT_ERR related tests), the 
self-hosted framework implementation (selfhtml.js, selfxhtml.js and svgunit.js for HTML, XHTML and 
SVG respectively) called Document.cloneNode(true) on the host document.  Unfortunately, the behavior 
of Document.cloneNode is implementation specific.

This "fix" modifies the framework implementation to fallback to a brute-force document copy if 
Document.cloneNode(true) returns null (as Mozilla/Safari/Konqueror does) or throws an exception (as 
Opera does).  IE 6 does clone the document on a call to Document.cloneNode(true), so it does not call 
the fallback code.  The fallback code calls DOMImplementation.createDocument which was introduced 
in L2 Core so it is possible for a conformant L1 Core implementation to fail the tests, but it is unknown 
if there are any browsers that fall into that category.

The problem does not affect the JSUnit hosted tests which use distinct IFRAME elements for each loaded 
document.