Basic arithmetic over Rational{Bool} doesn't work

[jiahao]

julia> true//true * true//true
ERROR: checked_mul not defined for Bool
 in * at rational.jl:188

Similar errors are thrown for the other basic arithmetic operations -, +, /, , ...

I'm not quite sure how arithmetic for this type ought to work. Note that not all arithmetic over Bools is closed, e.g. true + true == 2

[TotalVerb]

Are there any applications for Rational{Bool}? The integers mod 2 are a field already, so fractions aren't needed. Bool is not quite the integers mod 2 anyway because of addition behaviour.

[nalimilan]

I fixed this (without knowing) in #15294. It probably used to work before rationals switched to checked arithmetic recently:

julia> true//true * true//true
true//true

julia> true//true - true//true
0//1

julia> true//true + true//true
2//1

julia> true//true / true//true
true//true

julia> true//true \ true//true
true//true

I have no idea of whether this can be useful, but there isn't any reason not to support this either.

[tkelman]

We should probably add tests for these if someone wants them to continue working as they do at the moment.