Now using information about when pages are loaded to improve the record and replay layer's tab mapping.  If we come across a record-time event that we need to replay, but whose replay-time corresponding frame we don't yet know, we check the record-time trace to see whether the page was actually loaded during script execution.  If yes, we check the replay-time trace for a corresponding load event.  Whatever tab housed the corresponding load event is mapped to the record-time tab, and thus used for the event we're about to replay.  This approach is flexible enough to handle not just straight r+r, but also generalization, since it doesn't rely on identical URLs or anything like that.  With this change, my layer on top of r+r is now able to handle multi-page interactions.