Changes

• Added an internal system to detect if an item has been prematurely deleted due to any reason (typically falling in lava in the middle of an effect).
• Various drop, remove_worn_item, and setnotworn functions now return boolean indicating whether the related item is gone, so the situation can be subsequently properly handled by the ensuing logic.
• Improved lava_effects function, as this is the main culprit of many of the above situations.
• Fixed various other memory bugs.
• Added a bit more debug information.