Switching back and forth between panes is done often enough to justify an
easier way than reaching for the six key.
# Last window like Vim.
bind ^ last-window
bind C-^ last-pane
+bind C-o last-pane
# Top and bottom.
bind J select-pane -D
bind K select-pane -U
# Swap panes.
bind o swap-pane -D
-bind -r C-o swap-pane -D
bind -r O swap-pane -U
bind w command-prompt -p "Select [<window>.]<pane> to swap:" 'swap-pane -s . -t %1'
# Swap windows.