[Merge] ~nteodosio/software-properties:valid-magic-wait-event into software-properties:ubuntu/master

[Nathan Teodosio]

> is there any reason we keep pooling for tokens when the option is not selected?

Since wait() blocks, interrupting that thread when the user selects the other radio button is a bit involved, as far as I know. But I'll investigate this option further.

> wouldn't it be simpler to make the status update conditional to the selected widget option rather than using events?

Do you mean something like: Once wait() returns,

- If magic button selected, call update_state as we do now.
- If token button selected, set a flag, and make on_radio_toggled consider that flag and call update_state if set.

? That seems good.
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https://code.launchpad.net/~nteodosio/software-properties/+git/software-properties/+merge/438313
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