Assume :nothrow in iterating over tuples

[jishnub]

On master,

julia> Base.infer_effects(iterate, (Tuple{Int,Int,Int}, Int))
(+c,+e,!n,+t,+s,+m,+u)

Since the indexing is only carried out for valid indices, it should be safe to mark this as nothrow. After this PR,

julia> Base.infer_effects(iterate, (Tuple{Int,Int,Int}, Int))
(+c,+e,+n,+t,+s,+m,+u)

[KristofferC]

Is is also valid to annotate iterate for Array with this?

[jakobnissen]

Not Array in general, as there may be uninitialized values that will cause it to throw. But maybe if the element type isbits?