XQuery 3.1 implementation

The pull-mode implementation of window clauses in FLWOR expressions has been rewritten, reducing memory requirements when performing windowing over a long sequence of items.

In previous releases, Saxon passed all the W3C XQuery 3.1 test cases, but there were a few discrepancies on error tests where the wrong error code was generated. In 9.9, for the first time, the generated error codes in all cases match the test expectations.