In coop it's often hard to get on the same elevator together, because
they're immediately triggered once the first player steps on it.
This cvar sets a delay (1 second by default) for the elevator to wait
before moving, so other players have some time to get on it.
If you like elevators/platforms that suck, just set it to `0` :-P
Currently only used in func_plat, if it turns out that other entities
are used for automatically triggered platforms, we'll have to adapt
those as well (I guess wait_and_change() is generally useful for that).
We're not bumping the savegame version because they should only break in
an uncommon corner case: *Coop* savegames created with clients including
this change will not work on older clients - SP savegames are not
affected and old savegames on new clients also still work.
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