Support for #380

[Thorium]

Added support for SQL-columns to be non-left-hand-side.
So you can do this:

    let qry = 
        query {
            for item in dc.Main.Products do
            where (item.ExpiryDate > item.ShipmentDate)
            select item
        } |> Seq.toArray

Columns are still going as is to SQL in where.
So you still cannot do .NET operations to columns, so instead of this:

    let qry = 
        query {
            for item in dc.Main.Products do
            where ((item.Id+3) > 10)
            select item
        } |> Seq.toArray

you still have to write

    let qry = 
        query {
            for item in dc.Main.Products do
            where (item.Id > 13)
            select item
        } |> Seq.toArray