lazy facet instantiation

[Paolo Carlini]

Howard Hinnant wrote:

>> For the next ideas for enhancements you come up with, I would suggest
>> trying to figure out by and large whether in principle can be
>> implemented in a binary compatible way, or not, and adding that  info to
>> Bugzilla.
>
> <nod>  I'm lacking history.  I'm half expecting responses like:  
> Yeah, we discussed that in-depth 3 years ago and it won't work for us 
> because of X.

Anyway, FYI, just "saved the proposal" as libstdc++/24881. Also added to
Bugzilla that [meta-bug] about basic_string, would be libstdc++/24882.

Paolo.