Extract or handle FedEx namespaced XML better

[csaunders]

Currently we are performing a gsub on all instances of the SOAP APIs version prefix. With the API change that happened on January 19, 2014 this resulted in creating invalid XML that caused a massive breakage.

An example of the invalidly subbed XML can be seen here.

Solution: The gsub is super aggressive and it would probably be better to just properly handle the namespace. Maybe having some 'version detection' to determine which namespace to use could be useful for reverse-compatibility reasons or something.

[rdaniels]

I'm having the same issue. With active_shipping (0.11.2) when i run the code directly it returns FedEx quotes, but when i run it from RSpec 3.0.0.beta1 test I get #<REXML::ParseException: #<NoMethodError: undefined method `[]' for nil:NilClass>