[PATCH] New stream buffer for cin, cout etc.

[Benjamin Kosnik]

>If you want, the following two lines can be removed from the
>final generic _M_underflow:
>
>+           if (__testout)
>+             this->_M_out_cur = this->_M_in_cur;

Ok. I'll test with this, thanks, and if it's ok I think I'm just going
to put this in. This patch is already big.

best,
benjamin