This bigtime space promoter could get the Horsehead Nebula in a flying mare—but pinning a planetoid is tougher!           SPACEGRAM From: Jed Michaels, Ryttuk, Eros To: H. E. Horrocks, Interplanetary Amusement Corp., Cosmopolis, Earth I QUIT, YOU BALLOON BRAIN.                     JED ROCKET MAIL (Second Class) Dear Michaels: Your last message indicates you wish to leave the employment of the Interplanetary Amusement Corp. Under our employee policy, this is allowable, effective upon completion o