Add count support. Act more like XT.Data.fetch()
Keep the result consistant.
Merge branch 'exclusive_items' into 4_5_x_working
Add group by, fix order by
Get group by and order by to work with XM.XdrupleCommerceProduct
Fix order by by wrapping unions in subquery table.
Merge branch 'exclusive_items' into 4_5_x_working
Add etag support.
Fix etag error. Expose _fetch() so it be used in xdruple ext.
Merge branch 'exclusive_items' into 4_5_x_working