DPath: fn:namespace-uri() Unsupported Function

When running the recently-created fn:namespace-uri tests against the dpath-with-serialization2 branch, all tests fail with the following:

[error] Schema Definition Error: Unsupported function: fn:namespace-uri

{xmlns:fn='http://www.w3.org/2005/xpath-functions'}

[error] Schema context: element.e3. Location line 39 column 88 in file:/home/efinnegan/Projects/daffodil/daffodil-test/target/scala-2.10/test-classes/edu/illinois/ncsa/daffodil/section23/dfdl_functions/home_schema.dfdl.xsd.