[PATCH 2/6] Factor out color settings to cg-Xlib

setup_colors sets color variables from COGITO_COLORS, and
adds a sed script for diff colorization to color_rules.

Note that this changes the default colors a little from the
ones in cg-diff: in particular there's no bold any more. Bold
isn't really necessary if the "less search" thing in the new
cg-diff/cg-log is used (and bold is really ugly in
gnome-terminal :-) ).

Signed-off-by: Dan Holmsand <holmsand@gmail.com>
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