Small buglet related to autogeneration of limits

[Benjamin Kosnik]

> However note that all the rest of the library was compiled with my
> CXX=/mypath/c++, only the script for doing the limits fell back
> to the system's default g++.
> 
> So the problem was more one of inconsistent use of compilers
> between the main make system and the script to determine the limits.

Noted. This is no longer being generated at build time, but at configure
time. And CXX is now being exported, so I think this problem is fixed.

Just to be sure though, I'll try and put up a 2.90.9pre1 by tomorrow
afternoon. Perhaps you can try that?

thanks,
Benjamin