Various fixes for data migration:
Various fixes for data migration:

Change to after_save callback so that depreciation_entries.count works.
Instead of self.save (causes infinite loop), use update_columns.
Remove rescue clause so that errors aren't hidden.
Fall back to depreciation_start_date if current_depreciation_date is nil.

camsys/transam_accounting,camsys/transam_accounting,camsys/transam_accounting,camsys/transam_accounting