int drop(silently)
int silently;

This function must be defined by all objects that want to control when they
can be dropped. if 'silently' is true, then don't write any messages.

drop() should return 1 to prevent dropping. This is the opposit
of the get() function. That is because if drop() is not defined, it will
always be possible to drop an object.

If the object self-destructs when drop() is called, be sure to return 1,
as the destructed item surely not can be dropped.

Similarly, if drop() is called in another object, always test if the object
did self-destruct, as the object variable will turn to 0.