It's that time of year when urban gays across the nation begin making their resolutions.  Some may vow not to use their credit cards anymore.  Others might delete their Manhunt profiles and pledge to stop randomly hooking up with anyone who thinks they're hot.  A goodly number, though, have probably resolved in the last few weeks to lay off the Devil's Dandruff. The Bolivian marching powder. The booga shuga.  You know — blow.  Just to give you all a hand in sticking to your guns, we offer this field guide to the great leveler of personalities that is cocaine.