Pool and debug settings always are true

example:
ORM.connect("mysql://something:nothing@beep/boop?pool=false&debug=false", ...)
will still set debug == true and pool == true because calling the boolean constructor on a non-empty string always yields true. 

This fix simply checks the val of debug and pool, and if they are falsy, sets them to false, or true otherwise. (still maintains the null-defaulting case).