Review Board issue 1440: comment flag not visible in view diffs
Some miscalculation in rb javascript may cause a comment flag not
to be shown in the diff view.  The comment is still present in the
DB and is shown in the reviews view.
Also improved the code around guessRowNum, so it may be a bit speedier 
if the commented line is close to the row being examined.

Performed UT and Integration Testing using firebug.

Verified that the initial issue reported by end user is fixed for their diffs.