Implementation of multiple buckets handler
- Uncommented and changed a bit the lines of Casimir's redefinition of bucket:bucket_empty in ./minetestforfun_game/mods/bucket/init.lua to implement multiple buckets handle system, commented in an old commit (it was buggy, or something). The system has been modified a bit to prevent bugs from incompatibility between carbone's api (which the definition has been copied from) and minetestforfun_game's one.