Validates Icelandic postalcodes. By default checks against (prefetched) list containing all Icelandic postalcodes. Live check (against, by default, the official list) is available by switching $strong (2nd parameter) to true. $dataFile will be rewritten with the data retrived from $url in $strong mode
User can provide his own datafile if he wishes and/or own "official" list.
the postcode to be validated
optional; check against the official list (default off)
Validation according to http://www.hagstofa.is/?PageID=1474
Note: Icelandic SSN (Social Security Number) is on the form ddmmyy-xxxx. Here we strip the "-" char from the string (if present) and/or spaces in our match. Note: PASS IN STRING, NO EXCEPTIONS! SSN with leading zero (passed as integer) will NOT get validated!