Rock legend Gregg Allman has been cleared by doctors at the Mayo clinic to go ahead with a book signing tour.  Allman had delayed the tour after suffering from an irregular heartbeat following a recent hernia surgery that was related to his 2010 liver transplant, and underwent a series of tests at the Jacksonville, Florida clinic last Friday.  Allman, whose new memoir, "My Cross to Bear, " came out last Tuesday.  The 62 year-old will begin the book-signing tour next Monday in Atlanta before moving on to Nashville, Chicago, LA and New York City.