zero-alloc cache (was Re: [v3] Fix PR libstdc++/10276)

[Benjamin Kosnik]

>Thus:
>
>keep  explicit basic_istream(__streambuf_type* __sb);
>
>add   explicit basic_istream(__streambuf_type* __sb, __locale_cache<_CharT>* __lc);
>
>What do you think?

You are right. This would be the way to go, if this is the way things
are going to be done.

>Please don't :), I am hoping for an interface that can be used for
>other (global) ostream objects too, not just the standard streams.

Yep. I believe I understand what you want.

>I've thought of this before though; it would be nice to have
>an extention that allows one to free these memory pools,
>solely for memory leak testers.

More allocations choices would really be nice. If there was a persistent
allocator (perhaps even an __extern_alloc(size, alignment) things could
be cleaner.)

-benjamin