Add restrictions to prevent the player from short-circuiting or skipping most of the quest

[copperwater]

This doesn't have to wait for any particular quest overhaul to be completed. Includes:

• prevent horizontal teleportation in quest locate and quest goal levels if the nemesis is alive (this may be a good opportunity to implement conditional-notele flag)
• restrict [downwards] levelport in quest until nemesis is dead
• make most quest levels nondiggable