Add a visitor for easily traversing QueryFilter objects

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This is to allow non-sql datasources that have sql-like filtering capabilities 
to 
inspect QueryFilters without instanceof checks all over the place.  A patch has 
been included that adds the visitor, adds a simple default implementation for 
extension and rewrites the SqlDataSourceHelper to use the visitor.

Original issue reported on code.google.com by gak@google.com on 23 Oct 2009 at 10:24

Attachments:

• visitor.diff