Fix bug #3963 (Home/End goes to start/end of entire line, not just current line-wrapped segment)

Fix bug #3963 -- For Home, use new CodeMirror command that joins "goLineLeft" (line-wrap aware Home) with the "smart home" indent-aware behavior we still want.  See discussion here: https://github.com/marijnh/CodeMirror/issues/1544#issuecomment-49494252.