Dft namespace fix

[doolse]

Fixes the case where:

<manifest xmlns="http://www.imsglobal.org/xsd/imscp_v1p1" xmlns:eps="http://eps.pearson.com/xsd/item-metadata">
 <xml xmlns="http://eps.pearson.com/xsd/item-metadata"/>
</manifest>

comes out as:

<manifest xmlns="http://www.imsglobal.org/xsd/imscp_v1p1" xmlns:eps="http://eps.pearson.com/xsd/item-metadata">
 <xml/>
</manifest>

because the non-prefixed namespace matched the uri of an parent prefixed namespace. It should only ignore the namespace if declaration if it matches exactly.