Implement "pushwall can't move" sound
Issue #176
new
If you try to activate a pushwall whose movement is blocked, it sounds like a normal wall. E.g. the gold key shortcut on E6L8 cannot be detected from the outer hallway until opened. This differs from vanilla, and makes certain puzzles more difficult, such as the ghost area of E6L10.
This is what pull request #5 is about. Turns out to be a hard problem due to how the engine works, but I will definitely be trying to fix it. ECWolf's current behavior is definitely wrong, but it's wrong because if you play vanilla at 70Hz it can be hard to hear that sound at times. (Locked doors are supposed to make it as well.)