Comment 18 for bug 1527342

Thanks again Bill! I test the following:

- When user sets the circ history to enabled, history is now saved in action.usr_circ_history
- When the transaction is deleted, either through the purge history script or a direct database deletion, the circ id is set to null in the action.usr_circ_history row
- CSV download works correctly, both before and after the source circulation is deleted.
- The search history tagging continues to work as expected, both before and after the source circulation is deleted.
- When the patron is deleted, their action.usr_circ_history rows are removed.
- When the patron disable circ history tracing, they receive a warning. When they click through the warning, their rows in action.usr_circ_history are removed.

Merged to master for inclusion in 2.10