A bunch of spectator-joining-round tweaks.

* Re-enable the flashing-set thing on attempting to join with the item key. I spoke to Sal privately about this - turns out some keys ALWAYS send key presses instead of only sending one, and shift - what I have item bound to - is one of the problematic ones.
* Make the no-joining-game-after-20-seconds thing happen 20 seconds after the TIMER has started, not the level (ie, take starttime into account)