Debian, Berkeley DB, and AGPLv3

Bitcoin has been on the long road to eliminating BDB for some time. It is now no longer used for any of the network operations— it's only used for the local wallet code.

The decision to migrate off of BDB was unrelated to the licensing change— it was primarily driven by performance overall, performance regressions in new versions, reliability, and file format stability issues, but the licensing change would have done it in for Bitcoin if these other things handn't.