Saxon XSLT and XQuery Processor

When an attempt is made to add a namespace node to an
element, and the namespace node uses a prefix that is
already in use for the element name, but with a
different URI, Saxon reports an error. For example,
with Saxon 7.2, the following fails:

<ns:e xmlns:ns="nsone.uri">
<xsl:namespace
name="ns">nstwo.uri</xsl:namespace>
</ns:e>

The same failure occurs in Saxon 6.5.2, if the
namespace node is created using <xsl:copy/> or
<xsl:copy-of/>.

This should not fail, because technically according to
the specification, a prefix for the element name is
only created at serialization time (or namespace fixup
time in XSLT 2.0), in other words no prefix for element
<{nsone.uri}e> should be allocated until the namespace
node has been successfully created.

The error message is "Cannot create two namespace nodes
with the same name".

Applies to 7.2, 6.5.2, and all earlier releases.

Test cases: nspc39, nspc40