[z-machine] Different 1.1 proposal: put_prop and get_prop

[Ben A L Jemmett]

> Do any story files out there actually try to do this?

None that I know of for put_prop (Zinc will halt on such an operation);
get_prop is called in this manner by Christminster though.  It's looking to
see if a certain property exists on the object, and so doesn't care about the
value returned as long as it's non-zero.  This tripped me up; I was returning
0, and the game played but without an NPC (central to the story, of course,
and unbeknownst to me until we got the bug report).

Regards,
Ben A L Jemmett.
(http://web.ukonline.co.uk/ben.jemmett/, http://www.deltasoft.com/)