made a special case for typing with BR as the selection (as after an InsertBreak.)
made DEL and BACKSPACE at the beginning and end of a text node
fixes bugs 3742 and 3756 (with permission from choff and gkostello)
git-svn-id: svn://10.0.0.236/trunk@24209 18797224-902f-48f8-a5cc-f745e15eee43