Add dedupe() method for a field mapping. This assures that the value is unique, even if source data contains duplicates. Commonly used for usernames. Uniqueness is currently achieved by appending a number (e.g. example1). In the future we can expand to custom replacement patterns such as email address: sally1@example.com. Dedupe can be used on any mapping.

Change highwaterField into an array containing 'name' and 'alias' elements. Needed in order to generate valid :criteria replacement

#770064 by moshe weitzman. Better feedback msg. also exceptions/failures now count toward the itemlimit