[RFC] libstdc++/6720 and libstdc++/6671

[Paolo Carlini]

> ext/algorithm includes <algorithm>
> If this is changed to include "algorithm" will the preprocessor include
> ext/algorithm from the current dir, or spot that that's the current file
> and then proceed to look in the system dirs, finding the intended header?

I think Zack's idea could be adopted for the includes present in the
/standard/ headers, not for those in the /ext headers.

Paolo.