add query condition support for pagination.

[jnduan]

I think this is useful.

Person.pages({age: orm.gt(3)}, function(err, pages) {
        console.log("Total pages: %d", pages);

        Person.page({age: orm.gt(3)}, 3).order("name").run(function (err, people) {
            // should get you page 3, which means people who's age is greater than 3 from index 20 to 29 (ordered by name)
        });
})