[Qexo-general] Qexo parser improvements

[Per Bothner]

I checked into the Kawa CVS repository some improvements to
the Qexo lexer/parser so it can cleanly and generally handle
double-lexeme tokens, such as <define function>.  The latest
XQuery draft has many of these, in order to avoid reserved
tokens.

As part of this change, I also implemented the updated syntax:
declare namespace name = "URI"
default element namespace = "URI"
--
        --Per Bothner
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