ls color backwards compatibility

[Mikel Ward]

Hi

I've noticed recently that ls --color is using new colors for some
directories, apparently due to the new "tw", "ow", and "st" labels.

I don't like these, so I want to turn them off.  To do so, I added
settings for them to my LS_COLORS environment variable, e.g.

export
LS_COLORS='no=00:fi=00:di=00;34:ln=00;35:so=00;00:do=00;00:bd=00;00:cd=00;00:or=00;31:su=00;00:sg=00;00:tw=00;34:ow=00;34:st=00;34:pi=00;00:ex=00;32:'

This works fine on my system with coreutils-6.9, but with my older
system that uses coreutils-5.2, I get errors like:

ls: unrecognized prefix: tw
ls: unparsable value for LS_COLORS environment variable

I would expect:
1) ls only uses the colors specified in LS_COLORS (i.e., if I don't set
any value for tw, it should appear normal, not colored)
2) ls skips labels it doesn't understand, so I can specify labels like
"tw" for newer versions of ls and have older versions ignore it

Mike