- Add warning log level
- Change debug_log_level setting to enumeration string
- Map Irrlicht log events to MT log events
- Encapsulate log_* functions and global variables into a class, Logger
- Unify dstream with standard logging mechanism
- Unify core.debug() with standard core.log() script API
On calling clear_redistered_biomes the registered_biomes table is cleared
by creating a new empty table, but the pointer is not updated to point to
the new one. So after calling more register_biome, the registered_biome
table always contains 0 items, which is an error. Instead, the table is
cleared by removing all its items so the pointer (minetest.registered_*)
remains valid.
