[boost] License blanket permissions

Doh! When we were getting permission from library authors to put the Boost License on their works, we forgot to get permission to upgrade the license, if and when there is ever a 2.0 revision (or a 1.1). There's no forseeable need to change the Boost license, but we hope this software will have a longer-than-usual lifespan and unforseen events always come up eventually. So, we're going to begin a project to collect authors' permission to upgrade the license on their work, as necessary. Naturally any new license would conform to the Boost license requirements, and so would be substantially similar in spirit to the one we have now. -- Dave Abrahams Boost Consulting www.boost-consulting.com