This is a change-history and list of contributors to the script.

2012.10.14 by Joel Thornton

Improved compatibility with respect to comments migrated by a previous version of this script.

2012.09.28 by David Schnur

Greatly optimized Github API usage, allowing the script to process several times as many issues before reaching the API's hourly rate-limit.
The script now tries to avoid hitting the Github API's rate-limit part-way through processing an issue, to avoid leaving it in an incomplete state.
Improved support of duplicate / merged issues, by detecting the 'merged into' update and generating a Github comment pointing to the parent issue. The automatically-added 'issue x is a duplicate of this issue' comments are now filtered out, since Github already shows a reference when the duplicate links back to the parent.
Added migration of Google Code statuses like 'invalid', 'wontfix' and 'duplicate'; these now map to the matching Github tags.
The script now accepts Github projects in the form user/project, where user can be an organization or a different user from the one running the script. This still requires that the user running the script have enough permissions on the repository, of course.
Added an option to keep issue numbers in sync, by handling cases where Google Code skipped an issue number.
New issues are now marked closed after all comments have been added, to better mimic the order of that update in most real-world cases.
Added an option to automatically assign issues that have an owner in Google Code.
Added an option to omit migration of Google Code Priority labels.

Comments containing percent-signs are no longer added repeatedly when the script is run multiple times.