Fix word list speed in reader setup dialog

I don't think adding "Faster" to the method name helps...I think it would leave me wondering "faster than what" and whether there is a slower version somewhere and when I should use which one.

Rather it would be helpful to add a comment explaining why the longest word is passed to this method...that we're approximating our calculation of how many columns will fit for performance reasons.

Is there a reason why the code to figure the longest word couldn't be part of this method? Then it would be secret from the rest of the code exactly how we improved performance,  and we could try other tradeoffs later without affecting anything else if we find the columns are sometimes  too narrow. For example, if we one day decide to measure the 10 longest words, or not to count diacritics, or do a special hack for indic languages, or something like that, ideally only this code will change.

(Not saying it MUST be done that way...but if there's a reason to compute the longest word elsewhere it would be good to document.)