Fixed color -> xml and xml -> color in libxfce4mcs

[Jasper Huijsmans]

Olivier,

I was working a bit on the backdrop dialog to use a background color and
I noticed that the color was saved as type "string". This resulted in
rather interesting effects when I load the file from uninitialized color
values :)

Anyway I changed libxfce4mcs to save the correct type. Then I found that
made the manager hang on startup. So I changed the color parsing code as
well. It seems to work for me. Could you have a look and see if the
fixes are correct?

	Jasper

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