Proper failure messsage

In some cases script can fail *before* $BAG_LOG is created.
`nogemeente` parameter and improved error handling

* In order to avoid re-creation of `gemeente*` and `adres` tables during
  manual file processing, new parameter `nogemeente` added;
* Changed `RET` into `DOSQL_RET` variable within `dosql` function, it
  seems that otherwise it is affecting main code, causing improper
  error reporting.