At first glance, this looks like a rather pleasant alternative to the Millennium Bridge - a verdant, undulating span like nothing else in London. But look at what's written along the side and you may feel your gorge begin to rise. The Diana Memorial Bridge is one of dozens of abandoned London schemes in a long-running thread on skyscrapercity forums. These include an X-rated erotic gherkin, a bulbous colander for Trafalgar Square and, our......