patch for color_properties assignment

[John W. Eaton]

On  7-Jul-2007, Shai Ayal wrote:

| I attach a patch to fix color_property assignment.
| 
| As discussed earlier on at least 2 other threads, color_property and
| radio_value are unique in the graphics properties objects in that
| their set of allowable values is defined at runtime in their
| constructor. This in turn means that assignment of new values to these
| objects cannot be done by converting an octave_value object to them
| with a constructor, but rather using assignment:
| instead of
| 
| color_property color("aa|bb|cc");
| octave_value ov("bb");
| ...
| // don't use this -- it will destroy the old color definition and
| throw an error!
| //color = color_property(ov);
| // use assignment to keep old definition and give no error
| color = ov;
| 
| this patch adds the
| color_property& color_property::operator = (const octave_value& val)
| operator to facilitate this syntax, and also fixes the assignment in
| line_properties

OK, I think I finally understand the problem here.  I applied this
patch.

Thanks,

jwe