convert_roundcube_mysql2sqlite needs better logging

Hi,

The convert_roundcube_mysql2sqlite currently outputs errors like:

Successful creation of roundcube cp_schema_version table

Successfully saved version 0.7.2 to cp_schema_version tablerm: cannot get current directory: Permission denied

Successful creation of roundcube cp_schema_version table

Successfully saved version 0.7.2 to cp_schema_version tablerm: cannot get current directory: Permission denied

It would be very helpful if the output produced progress markers like "starting conversion of $acct" and output "converted $acct successfully" or "converting $acct had errors" so we would at least know where to start looking and/or testing when the user reports the above. Possibly work on this improvement when fixing case 61339 - convert_roundcube_mysql2sqlite never creates it's log file.