Smooth scrolling issues

[migueldeicaza]

• Smooth Scrolling: empty regions painted #249

• Smooth Scrolling: needs auto-reset to bottom #250

• Smooth Scrolling: selection broken #251

[migueldeicaza]

The issue is that we are only calling updateDisplay which in turn fills the attrStrBuffer with partial updates as the display is updated, and those gaps mean that we did not created attributedStrings from the text that is there.

One option is to not use the cached data at all, and eliminate the need for attrStrBuffer, and just compute on each use. But I also wonder if the attributed string is needed at all, or if we can go directly to the CTRuns.

[migueldeicaza]

Finished!