error returned from Capture interface does not contain position and is not wrapped

Sometimes it is useful to return an error from the `Capture(values []string) error` method. However the final returned parser error is not decorated with the position properly.

Actually the returned error is a v2.parseError but it does not contain a valid lexer.Position. Also the original error is discarded and just the message is kept instead of using the wrappingParseError type.

It seems like that the decorate function in setField (nodes.go:553) should do the job, but it does not use the tokens position. Also it just uses the parseError type instead of the wrappingParseError.