Restructure of CDR Code to Better Handle Transfers

This is a notification/documentation/late night equivalent of powerful sleeping drug,  for the changes I am about to commit into the trunk of Asterisk.

No doubt most people working with CDRs have felt that the Userfield is grossly inadequate to encode all of the details they would like to have. The problem is, how do you create a generic CDR engine that will satisfy different people on different systems with completely different needs?