`join` calls `done()` twice on the iterables

[lucasb-eyer]

As noticed by @ivarne in #9159. Here is a possible unittest for it:

# issue #XXX `join` calls `done()` twice on the iterables                                           
let                                                                                                 
    type JoinTest                                                                                   
        nnext::Int64                                                                                
        ndone::Int64                                                                                
    end                                                                                             
    import Base.start, Base.done, Base.next                                                         
    function Base.start(jt::JoinTest) jt.nnext=0 ; jt.ndone=0 ; 0 end                               
    function Base.done(jt::JoinTest, n) jt.ndone += 1 ; n > 3 end                                   
    function Base.next(jt::JoinTest, n) jt.nnext += 1 ; "$(jt.nnext),$(jt.ndone)", n+1 end          

    @test join(JoinTest(0,0), ";") == "1,1;2,2;3,3;4,4"                                             
end                                                                                                 

[ivarne]

That works! (or rather it fails)

I'll try to fix the join implementation.

[ivarne]

Hmm... This will be our first explicit test for join. It's probably time!

[StefanKarpinski]

Thanks guys. I wrote join a long time ago before we were in the habit of writing tests for everything.