GitHub usernames in maintainers field

[Ryan Schmidt]

I appreciate that we are making these changes slowly. This gives the buildbot time to catch up on other commits.

I don't want to commit all maintainer-to-GitHub changes in one revision and then cancel the buildbot build, as we did with the $Id$ removal commit, because valuable builds are being done by the buildbot as a result of these commits which I want to allow to happen.

The mega $Id$ removal commit also exposed a limitation of the GitHub git-to-svn gateway, which we are using on our server in the mprsyncup script. I reported the limitation to GitHub and they said they would look into it but I don't know if they've fixed it. I believe we can avoid triggering this limitation again by not modifying too many files in a single commit. If we hit the limitation again, manual intervention is required to throw away the Subversion working copy on the server, and then after the new working copy is checked out the portindexes get regenerated, which takes hours; I want to avoid going through all that hassle ever again.