Update read.output.R

[tonygardella]

read.output handles "start.year" differently than we normally do deal with dates (ie "2004/01/01").

#1785 was made to document the difference but we need a code change.

Mike made the comment: I'd prefer to fix the code than fix the documentation. I think we want the code to be flexible enough to read either character or numeric years, and then convert numeric years to character internally. I don't think we want to go in the other direction (char -> num) since pre-1000AD the leading zeros become important.

Tess responded: My edit to the documentation was mostly just trying to convey that it didn't have to be, and won't accept a full "yyyy/mm/dd" sequence. Some of the other functions (load_data?) need a full sequence.
I bet it does only take a character though. I can double check.