wxString is far slower than std::string (sometimes more than 20 times)

[Armel Asselin]

> Even with a reserve or resize it seems that the data change address all
> the time (but less often with std::string)
> Time wxString replace : 25343 OUPS !   Time std::string replace : 61
>
> Time wxString replace : 9741 OUPS !   Time std::string replace : 62
>
replace is O(n2) in wx implementation.

Armel