deque fails to meet 23.2.1.3.4-5 causing invalid iterators and extra assignments

[Paolo Carlini]

Steve LoBasso wrote:

>BTW I believe this problem also exists in the single parameter version of erase.
>
>erase(iterator)
>
Please provide a detailed analysis, possibly a testcase: of course, when 
I fixed the other overload I suspected that, but I failed to find values 
of size() and __position leading to similar problems.

Thanks,
Paolo.