Fix Underline + Color in TMUX (TERM=screen-256color)

When using TMUX normally the TERM environment variable is set to screen-256 color. Under OS X at least the terminfo for this terminal disables color and underline used together. The result is that programs such as emacs will display color but not underline text.

I found the following quick fix for this from Chris Johnsen.

$({ infocmp -x screen-256color;
    printf '\t%s\n' 'ncv@,'; } > /tmp/t && tic -x /tmp/t)