follow df-structures change to drawBuilding
core: generate SC_WORLD_LOADED for arena too
add NEWS entry for arena SC_WORLD_LOADED
fix renamed pregnancy_ptr/mystery to pregnancy_genes/caste
Update xml definitions.
Fix crash due to incorrect loop bounds in add-spatter.

This caused a buffer overrun bug if an ADD_SPATTER
reaction had any non-improvement outputs.
Track readable names of vmethod hooks for diagnostic messages.

Note that this changes the ABI of all plugins that use hooks.