C-g doesn't abort `add-require`

The same is probably true of other commands. If I invoke `ar`, start typing a namespace name, and then change my mind, `C-g` doesn't behave as expected.

I would expect it to either (1) go back to what I had before the command started or (2) abort the command and leave the ns form as it is now.

Instead, when I hit `C-g`, it leaves the `ns` form as it is now and then continues with the command (which means that it cleans up and evaluates the ns form). Evaluating the ns form is particularly problematic because I'm guaranteed to have an unfinished namespace name in there.