Fixed alcohol not affecting your stats (alcohol too strong now?)

Apprently, alcohol handling was using broken or outdated methods, which resulted in none of it's effects on your stats working.
Note that alcohol is now EXTREMELY damaging to your stats compared to what it was before (I don't even know how long this bug was around), because the debuffs from alcohol stack on top of the debuffs from alcohol counting as a powerful depressant. 
In fact, the debuffs from alcohol being a depressant are more damaging than the alcohol itself; perhaps alcoholic drinks could be given slightly higher STIM values to offset this.
Fixes  #5845 

EDIT: Also note that there are still a couple of entries in disease.cpp that use the outdated "p.[stat]_cur -=" method, I'm not sure if they work correctly as I haven't tested them.