Fix for my previous commit: color mapping is not 1:1.

Cons25 doesn't seem to use a straight 1:1 mapping to the ANSI colors,
but uses the same color numbers as at least used by syscons on i386. I
suspect if you change the definitions on a different architecture,
things may break? Not sure.

Add a small array to convert syscons-style color codes to ANSI
equivalents, which are used by libteken internally. I didn't notice this
bug, because I only tested my code with black, white and green, all of
them shared the same numbers.