getAttributeNodeNS().

- Move parseAttributeReplacements() and splitParts() out of the class
  (they can be simple functions), so they can be imported by
  TALCompiler and TALInterpreter.

- Remove a redundant key argument from doReplaceLoop() and
  doInsertLoop().

- Add an XXX comment warning that we don't check for z:replace on the
  documentElement.