E3S10: Make the lying-on-the-floor instances of Elyssa and Elynia upkeep=free
E3S7A.1: Add sound effect for the first gate closing
E3S7A.1: Fix the floor 1 "not the right corridor" warning event

 * Only run after Elynia has been revealed, preventing "cannot show
   message" warnings being emitted when moving units adjacent to the
   entrance block at the very start of the scenario.
 * Filter on tiles adjacent to any hex with the impassable overlay, not
   just U*, otherwise we never match the middle portion of a passage
   (Rr).

The event shouldn't run before Elynia enters the main corridor either,
but that case is already covered in a way: after she is revealed, there
are no tiles in the starting area that fulfill the SLF.
E3S7A.1: In-scenario prose revision
E3S12: Don't leak scenario-local variables to E3S13
E3S7A.2: In-scenario prose revision
E3S7B: In-scenario prose revision
E3S7B: Extend SUFs for Cron's crush-everything event handlers
E3S8A: In-scenario prose revision
E3S8B: Prose formatting change
E3S8C: Fix typo
E3S8C: In-scenario prose revision
E3S8D: In-scenario prose revision
E3S9: In-scenario prose revision
E3S10: In-scenario prose revision
E3S11: In-scenario prose revision
E3S11: Update end credits
E3S12: In-scenario prose revision
E3S13: In-scenario prose revision
E3S13: Storyscreen prose revision