The price of Bitcoin, the bizarre digital currency, has been skyrocketing. And everyone's calling it a bubble. But it's not like most other bubbles. Art Cashin, UBS' man on the New York Stock Exchange trading floor, contrasts the Bitcoin bubble to the Dutch tulip mania of the 17th century. Here's Cashin: Trading Tulips In Real Time – It is rare that we get to see a bubble-like phenomenon trade tick for tick in real time. Usually it's kind of regional aggregate pricing like real estate reports. But, all that may be changing – before our very eyes – quite literally....