[PATCH] XInclude transformer does not handle fallback correctly

When using the <xi:fallback> element, the XInclude transformer returns a
not-well-formed document.

Example:

<root xmlns:xi="http://www.w3.org/2001/XInclude">
<xi:include href="this_file_does_not_exist.xml">
<xi:fallback>
<element>This should be here if the file was not found</element>
</xi:fallback>
</xi:include>
</root>

returns this, if the included resource does not exist:

<?xml version="1.0" encoding="ISO-8859-1"?><root
xmlns:xi="http://www.w3.org/2001/XInclude">

<element>This should be here if the file was not found
</xi:include>
</root>