Bind Ctrl+Left to backward-word (and Ctrl+Right to forward-word)

Binds some additional sequences to (emacs-)backward-word and forward-word. The problem is that terminfo doesn't know about Ctrl+ArrowKeys, so one has to resort to using rough sequences. The sequences were copied from Debian's `/etc/inputrc` (readline configuration), so it should be fairly portable. It works in xterm and rxvt terminals, it doesn't work on TERM=linux (virtual console) as Ctrl+Arrows seem to send the same sequence as Arrows alone.

http://zshwiki.org/home/zle/bindkeys
http://sources.debian.net/src/readline6/6.2+dfsg-0.1/debian/inputrc?hl=44#L44