Issue with namespace prefixes?

Hi,

I ran into issues using the Calais.enlighten method. I took a look and it seemed that Nokogiri was having problems with some of the XML nodes that had "c:" namespace prefixes. I changed the Calais::Response to have the prefixes and all the tests now pass. 

This is with ruby-1.9.3-p286 and Nokogiri 1.5.6.