`diesel print-schema` generates invalid code when automatic column renaming occurs

[sgrif]

This is generated when you run diesel print-schema against our test suite's schema

table! {
    with_keywords (fn_) {
        #[sql_name = fn]
        fn_ -> Int4,
        #[sql_name = let]
        let_ -> Int4,
        #[sql_name = extern]
        extern_ -> Int4,
    }
}

[Eijebong]

Fixed by #1252