[boost] 1.53 schedule change

Hello everyone, I just noticed that I forgot to account for Christmas when setting the schedule for 1.53. I've adjusted it so that the deadlines for new libraries and major changes are a week earlier (as specified on the release schedule page). Sorry about that. There's still 3 weeks before the new library deadline, but please let us know soon if you have a new library for 1.53. thanks, Daniel