Bug 11237: Update explanation for pref AcqItemSetSubfieldsWhenReceived

Bug 11237: Update explanation for pref AcqItemSetSubfieldsWhenReceived

This patch improves the description of the AcqItemSetSubfieldsWhenReceived
system preferences to clarify that it applies to updating items
during order receipt, if those items where created when the order was
placed.

Test plan:
Update the updatedb entry and search the pref in the admin module.
The explanation should have been updated.

Signed-off-by: Mark Tompsett <mtompset@hotmail.com>
Signed-off-by: Kyle M Hall <kyle@bywatersolutions.com>
Signed-off-by: Galen Charlton <gmc@esilibrary.com>