Improve and optimize the autosize text area widget.

Review Request #209 — Created Jan. 24, 2008 and submitted — Latest diff uploaded

Review Board SVN (deprecated)
The autosize text area widget we use in the review request page and comments dialog got really slow with large amounts of text. We used a pretty crappy but commonly used method for this widget. Now we use a sane method where we keep a proxy element that is the same shape and style of the text area but wraps and has a dynamic height. We use this to calculate the correct height for our text area. This seems to improve the speed considerably and simplifies the code.
Tested on Firefox and IE6. Works correctly on both.