Colored reduction cannot be disabled

[Jiri Srba]

Open any colored net example (e.g. philosophers) and open the query and use "advanced query dialog".

Now run the verification with colored reduction enabled and it adds the switch:

--col-reduction 1

when calling the engine verifypn (see the command line output what are the parameters). This means
that the aggresive reduction is enabled (but this is the default option, so this switch is not necessary).

Now disable (untick) the colored reduction and the switch --col-reduction is missing completely
(and by default the reduction is enabled).

The correct behaviour is:

1. if colored reduction is enabled, do not add any --col-reduction switch, or add --col-reduction 1 (default option anyway)

2. if colored reduction is disabled, add the switch --col-reduction 0

If you run verifypn -h, you can see the correct switches that the engine is using.