Deal with ambiguities in multiple definite object resolution

Right now, GET THE TWO MATCHES causes problems when there's no obvious match for THE TWO MATCHES because, say, there are three matches with different attributes available for the taking.

This patch resolves the problem by just printing:
I don't know which ones you mean.  Can you be more specific?

Please read the comments and diff carefully before applying, because I doubt I've implemented it the best possible way.  The biggest issue I have with this is that the question "Can you be more specific?" implies some sort of ability to process a partial answer as the next command, which it doesn't.  Maybe a better message is in order, or maybe there's a way to let the next prompt be an arbitrary noun phrase to fill in.

If you have changes you want me to make, I can do that before you pull this in.