(list-colors-display): Add new arg buffer-name.

(list-colors-display): Add new arg buffer-name.
Use it.  Fix docstring.  Replace code for identifying duplicate
colors by the name with call to `list-colors-duplicates' which
identifies duplicate colors by the value unless the color
is one of special Windows colors.  Set truncate-lines to t.
Print sorted duplicate color names on each line.  Indent to 22
\(the longest color name in rgb.txt) instead of 20.  Optimize.
(list-colors-duplicates): New function.
(facemenu-color-name-equal): Delete function.