[boost] [1.40.0] Release plans

I've been missing in action for most of the month, working on C++ committee stuff. Sigh. Rather than set a new release schedule for 1.40.0 right now, I'm planning to spend the next week or so looking at the state of the release branch, and pestering folks as needed. As that process proceeds I'll get a better sense of what a reasonable schedule would be to finish the release. In the meantime, the release branch is still open for merges as long as they are stable on trunk tests. --Beman