Text to go in the release notes:
In the past, if a patron had any credit existing on their account (newly added, or pre-existing), if debts were present then the credit balance would always be immediately applied to the debt. This functionality was inadvertently removed during refactoring efforts which debuted in 16.11.
This patch adds code to restore the functionality and allows it to be optionally applied to the system via a new system preference, `AccountAutoReconcile`.
Note: The new preference defaults to the post 16.11 behaviour, if you wish to restore the 16.11 functionality then you will need to update the preference after the upgrade.