Can't use IS NOT expression in Postgres

[adriangb]

Using Expr::is_not(<expr>, Value::Bool(Some(false))) generates SQL like SELECT * FROM table WHERE col IS NOT $1 which is not legal in Postgres (you'd get a ERROR: syntax error at or near "$1" if you do PREPARE q AS ...).

I don't see how SeaQuery can easily fix this, but it might be nice to mention in docs and provide alternatives. In particular, hardcoding the RHS as Expr::expr(SimpleExpr::Constant(Value::Bool(Some(false))))) works.