[v3] typeinfo tuning

[Benjamin Kosnik]

> Does exporting some of these symbols and vtables from the library mean
> we're less able to change them?  I'm not confident all ofthe C++0x
> bits are entirely stable yet.

Yes, it does. What are the new exports that concern you? 

There are some things I purposely did not include. For instance,
<regex>. Some of <future> can be further optimized for the void
specializations, but I did not do that to give implementation
flexibility in the future. 

> I see you've given future_base::_Result_base a virtual destructor, is
> there a specific reason for that?  

Yes...

> Destruction should always be via
> the virtual _M_destroy function and so 'delete' is called in the final
> overrider, where the static type and dynamic type are the same. The
> virtual destructor adds unnecessary overhead, though it's probably
> negligible.

Yeah on negligible. I don't see the addition as a correctness issue,
right? The __future_base nested classes don't seem to be changing all
that much, but I will defer to you if you are uneasy about specific
changes.

Doing this may allow the control of all vague symbols in <future> for
standard instantiations in the future. 

best,
-benjamin