[metapost] augment drawoptions

[Taco Hoekwater]

Stephan Hennig wrote:
> Taco Hoekwater schrieb:
>> Stephan Hennig wrote:
>>> As can be seen macros _op_stack_A to _op_stack_C are defined, but empty,
>>> whereas _op_stack_D is of type "tag".  Is there a way to completely
>>> remove a macro, i.e., make an identifier a tag again?
>>    save <macro>;
> 
> But does that save memory?  

Only at top level, true. A primitive could be provided to remove
values without saving them, but in that case something that saves
in a non-destructive way may be useful too. Comments welcome.

Best wishes,
Taco