Returns the value for a given statName that belongs to the drink object.     The entity may be an object pointer or object keyword. The statName may be     any one of the following stat IDs:
          poisoned        affectDrunk         name            affectHunger         colour          affectThirst         maxCapacity         usedCapacity
      Example:
      @usedCapacity = %drinkGetStat( @o, usedCapacity )  |