Allow the country field in addressbook to be specified as either the ISO 2 character country code or the netsuite enumeration value.

ex: `addressbook.country = “_unitedStates”` and `addressbook.country = “US”`
have the same end result.

source: 
page 228 here: http://www.netsuite.com/portal/partners/integration/download/NetSuiteWebServicesRecordsGuide_2_0_0.pdf
> The following Country Enumerations and State Enumerations tables list Countries and States 
as defined in NetSuite drop-down lists and the corresponding enumeration to be used when 
populating these fields in Web services requests.
>
> Note: As a general rule, enumerations are simply camel-cased concatenations of the Country name 
as defined in the NetSuite UI.
>
> The Country Codes listed here are the ISO compliant country code string values returned 
when performing a search operation on entity records whereas the Schema Enumeration is the 
corresponding value used during a request.