"introduce no new bootstrap warning" criteria. was: Loop iv debugging, patch

[dewar@gnat.com]

<<If rewriting is 'too big a burden', I suspect that means the warning
is not 'easy to avoid', and so it should not be in -Wall.
>>

But if your criterion is that no use ever anywhere could be in the 
category of not "easy to avoid", that's a rather fierce requirement.

However, I suspect that most of the remaining warnings are indeed
fixable.