Activity receive_date is incorrectly updated to now when importing historical transactions
Contribution receive_date is incorrectly updated to now when importing historical transactions, see #1831 (closed) for more context.
Adding this line to addActivity() in CRM/Activity/BAO/Activity.php seems to fix:
$date = CRM_Utils_Date::isoToMysql($activity->register_date);
https://github.com/civicrm/civicrm-core/blob/master/CRM/Activity/BAO/Activity.php#L1708
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