What happens to an existing install, indeed? That's why this code hasn't been merged already. Likely, what happens is that Puppet, or you, may search for files that were bucketed using the old hash algorithm, and not find them. What happens then, I'm not really sure: I didn't really learn how file bucketing works before doing this patch. All that anyone from Puppet Labs has said is that it's a definite migration concern. I was hoping someone else would know better than me how to fix that concern but no one has stepped up. (No hard feelings meant.)

This particular branch was made from the puppetlabs/puppet master branch about a month before 3.0 was released. I haven't moved to 3.x yet, so here it sits.