Fix problem with non-working unbind of a rune key.
E.g. after the following commands:
bind "n" "FindNext"
unbind "n"
Observed result: "n" key still triggers FindNext action
Expected result: "n" key inserts "n" rune
On non-Mac operating systems, the default for CtrlLeft/CtrlRight
is now WordLeft and WordRight instead of moving the cursor to the
start and end of lines (now rebound to Alt-Left/Right by default).
Default keybindings are unchanged on Mac.
Fixes#1465