Saxon XSLT and XQuery Processor

The static type analysis and other compile-time checks
are not performed on the operands of the "is" operator.
This can have fairly unpredictable effects. In the case
encountered, it caused a call on the key() function to
fail with a NullPointerException.

Reported by James Cummings.

Source fix: add
operands[0] = operands[0].analyze(env);
operands[1] = operands[1].analyze(env);
to start of analyze() method in
net.sf.saxon.expr.IdentityComparison.