dirstate and improving the performance of hg-add

[David Schleimer]

> You are sidestepping my question :-). The question is about whether the default
> value of "warn" is actually relevant to your very demanding use patterns.

Sadly, yes it is.  We have existing examples of case-conflicting files in our history, and possibly our current tree.  We also have an occasional need to check out to local (non-linux) disks.  Among other reasons, lawyers look at code during discovery.  In particular, they tend to look at old code during discovery, so we need this on now and being able to change our minds later isn't good enough.

In addition, we aren't a pure linux shop.  We also have native code that runs on iOS, Android, and even Windows, though not in our primary repo.

--David