Code review comment for lp:~gary-lasker/software-center/handle-trans-cancel-lp1027209

Ok, I added the check for the launcher queue to be properly emptied for the various types of transaction end cases. The error case, where a "transaction-stopped" signal is emitted, needed a fix to clear the queue so I've added that as well.

Note that clearing the queue isn't strictly required as an item left there will have no ill effect (it's only functional when the corresponding package completes a successful install, and in this case it will "just word". Plus, it's not likely that many items would end up queued in here. Neverthess, it's clean and much nicer to clear it out for all cases, so it does that now.

Should be ready for re-review now. Thanks!