Sorting out the meta key.

Thanks to [this
thread](http://stackoverflow.com/questions/6778961/alt-key-shortcuts-not-working-on-gnome-terminal-with-vim)
I could get the meta key picking up in both tmux and vim.

As a result of this I now have the following shortcuts working properly
(at least on OSX).

*  __Meta+direction__ - swap split
*  __Meta+w__ - save file
*  __Meta+c/r__ - move no next buffer