Saxon SQL extension instructions

At the suggestion of Claudio Thomas [claudio.thomas@web.de], I have extended the sql:query instruction to allow the attribute disable-output-escaping="yes|no". This is useful where the database content being retrieved contains XML or HTML markup that is to be preserved in the output. Use this with care; it disables escaping for all the rows and columns retrieved, some of which may contain special characters such as "<" and "&" that do need to be escaped.

This change has not been tested.