Fix copying to xclip
Fix copying to xclip

Copying to clipboard was an issue, as the fact that it didn't generate
any output seemed to be an issue for tmux (bug?). Anyway, @procrat gave
me this tip, and it seems to work indeed. The fact that everything is
now always copied to X-clipboard doesn't really matter.

paretje/dotfiles,paretje/dotfiles,paretje/dotfiles,paretje/dotfiles,paretje/dotfiles