- Either adapt P_UseItems to the latest ZDoom changes or remove it. Currently it's just disabled.
- Make the botpath code use the new ZDoom iterators instead of the old copies of P_BoxOnLineSide, P_BlockLinesIterator and P_BlockThingsIterator

Code refactoring:
- Globally replace GAMEMODE_GetFlags( GAMEMODE_GetCurrentMode( )) with GAMEMODE_GetCurrentFlags( ).