changing genprop.awk to handle radio_values

[Shai Ayal]

As discussed in previous threads, to set radio_properties and/or
color_properties from an octave_value, an assignment should be
preformed, not a constructions. i.e.

radio_property rp("all|none|quiet");
octave_value ov("none");

// the right way, preserves the allowed_values
rp = ov;

// the wrong way, overwrites allowed values
rp = radio_property(ov);

Currently genprops.awk only allows for the "wrong way" when emitting a
"set" function:

##   void
##   set_NAME (const octave_value& val)
##   {
##     set_NAME (TYPE (val));
##   }
##

this can be fixed in one of the following ways:
1) don't change genprops.awk, and use an o or O modifier to write a
custom version of set
2) make genprop always emit an assignment "set" function:
##   void
##   set_NAME (const octave_value& val)
##   {
##     NAME =val;
##   }
##

3) add another modifier (say "a") to make genprops emit an assignment
set function
4) have genprop.awk automatically emit an assignment "set" function
(like in example 2) if TYPE is color_property or radio_property

all of these changes seem trivial, the question is, which road to take?

Shai