dirstate and improving the performance of hg-add

[timeless]

Joshua Redstone wrote:
>  First, doing a case-insensitive comparison of the path to be added against
> all existing paths in the repo, in order to warn about adding a file that
> might conflict with other files in the repo on a case-insensitive file
> system.

It seems like you could instead add a hash of a case folded lowercase
path reference for files to a dictionary.

If there's a collision in the hash, investigate.

I'm not sure if the cost tradeoff is a win, you're doing case folding
O(n) files and then n*O(1) lookups.