Add "Accept as solution" button to previous meta guesses

[benchen71]

If a solver has entered a number of incorrect meta answers, and I look at the wrong answer list for them, and then I decide that one of their answers is close enough, there is no way to accept that earlier answer as correct.

In the above image you can see "hoist a flag" and "raise a flag" (my originally intended answers were "hoist the flag" or "raise the flag") in the list. But the user then entered "bear a flag" as their final guess.

After seeing this, I added "hoist a flag" and "raise a flag" as acceptable answers. However, unless there is a caching issue going on, it doesn't look like the system checks prior meta guesses, just the most recent guess.

It might also be good if there were "Accept as solution" links on the list of prior guesses, too.

[mdirolf]

I definitely think adding the "Accept as solution" button to prior guesses would be a nice improvement - I'm changing the title of this issue to reflect that goal.

As for marking submissions as correct based on the content of a prior guess - that's also a good idea! But my gut is that the system is pretty far away from being to handle that. I'll do some checking to see how much work it'd take to make it possible, but I think that might end up being one of those things where the improvement doesn't justify the implementation effort. If it seems feasible, though, I'll open a separate issue for it.