*sh: add screen-256colors-italic terminfo

May as well use 256 colors everywhere, now that I have the necessary
terminfo entries on both of the machines that I use.

Signed-off-by: Wincent Colaiuta <win@wincent.com>
Vim: remove unnecessary t_Co setting

It seems the default (now 256) works just fine.

Signed-off-by: Wincent Colaiuta <win@wincent.com>