Enable to change pane with "C-t i"

Before this commit, it can be done by only "C-t C-i".
Change F4 to the 2nd prefix key

ref. http://stackoverflow.com/questions/10148449/multiple-tmux-prefix-key-combos
Merge branch 'tmux'
Behave some key combos as "<Esc>"

ref. https://twitter.com/rbtnn/status/485418077324980226
Only "kk" behaves as "<Esc>"

ref. https://twitter.com/anekos/status/485416150541402112
Merge branch 'vim'