-Wconversion versus libstdc++

[Paolo Carlini]

Joe Buck wrote:

>In the case of the containers, we are asserting/relying on the fact that
>the pointer difference is zero or positive.  But this has become a
>widespread idiom: people write their own code in the STL style.  If STL
>code now has to be fixed to silence warnings, so will a lot of user code.
>
Good point. About it, we should also take into account the recent 
messages from Martin, pointing out that many C++ front-ends do not warn 
for signed -> unsigned.

About the library itself, I'm also concerned by the weakness of our 
pragma system_header vs templates, which makes the whole warning game 
always very dangerous...

Paolo.