[Patch] Finally implement Matt's "recipe"

[Paolo Carlini]

Paolo Carlini wrote:

> Regtests are Ok on x86-linux and now I'm going to thoroughly check the
> patch on other platforms and verify that the performance are also
> still ok.

The posted version uses the wrong macro for wchar_t, sorry:

    s/_GLIBCPP_USE_WCHAR_T/_GLIBCXX_USE_WCHAR_T

otherwise, further tests are going well (also retested on char the slow 
versions).

Paolo.