performance patch for stl_vector.h

[Paolo Carlini]

Hi,
> We've found that the following patch to avoid allocating storage for 0
> length vectors is a significant performance win in our product. I'd like
> to get it folded back into libstdc++.
>   
Which version of GCC? I'm asking because in sufficiently recent versions 
of the library _M_allocate itself implements this optimization and not 
much remains to be gained...

Paolo.