Attempt to fix dhwty/flist-messenger#67

The selection no longer expands, but at the cost of the view jumping to the selection
whenever a line is added and there's a selection.
Make FLogTextBrowser scroll correctly all the time
Merge pull request #69 from kythyria/issue-dhwty-67

Fix peculiar interaction of scrolling, selection, and appending things to the log pane.