[boost] [1.37.0] Release branch closed except by permission, beta one week from today

The release branch is now closed for all changes except by permission from one of the release managers. The beta release is planned for one week from today. That's a three day schedule to provide a bit more time for QA reviews, and because it seems to work a bit better if target dates fall at the end of weekends rather than Fridays. --Beman