Simplify `A == B == constant` conditionals

[plafosse]

We currently do not simplify the case of Comparison with the result of a comparison. This is a straightforward optimization:

A cond B == 1 => A cond B
A cond B == 0 => A !cond B
A cond B == !(0|1) => False

[spoonmilk]

Fixed in 5.1.7629