Progress Indicator when converting custom fields during 4.4 upgrade

During the 4.4 upgrade, we now convert custom fields to store IDs instead of the direct values. In certain circumstances this upgrade can take a long time (a 200k issue instance with ~80 custom fields took about 30 minutes) but there is no indication in the logs that there is any work being done.

Could we indicate that progress is being made, perhaps a "Converting field X of Y" type of indication in the logs to let us know that the upgrade is still going ahead.