This is a niche-module in that its target group is those people who hack the source of perl. The supplied script "buildaperl" takes a patch-number or version and builds the respective Perl distribution. It can thus be used to find out which patch can be blamed for a particular change. This module is indispensable for every perl porter.
The only drawback is that you will most likely need the full Perl repository with all changes. This repository is currently around 700meg in size. This repository is worth every single byte though.