added new function to pad barcodes
-- expand_barcode
-- $barcode source barcode
-- $prefix prefix to add to barcode, NULL = add no prefix
-- $maxlen maximum length of barcode; default to 14 if left NULL
-- $pad padding string to apply to left of source barcode before adding
-- prefix and suffix; set to NULL or '' if no padding is desired
-- $suffix suffix to add to barcode, NULL = add no suffix
--
-- Returns a new string consisting of prefix concatenated with padded barcode and suffix.
-- If new barcode would be longer than $maxlen, the original barcode is returned instead.
Example usage:
UPDATE foo
SET barcode = migration_tools.expand_barcode(barcode, '21234', 14, '0', '');