tmux: 'C-b u' will join wrapped lines for urlview
tmux: making copy-mode act more like my emacs conf
tmux:osx - modify conditions for sharing clipboard

tmux will now only share the clipboard with the system if $DISPLAY
exists and 'reattach-to-user-namespace' is available in the $PATH.
tmux: cleaning up cygwin tmux config
tmux: share Linux clipboard with via xclip

The clipboard will only be shared via xclip if $DISPLAY exists.