LONDON.- The newspaper coverage was troubling: London’s huge international showcase was beset by planning problems, local opposition and labor woes — and the transport was a mess. It sounds like the 2012 Olympics, but this was the Great Exhibition of 1851 generating stories of late trains, unscrupulous landlords and dangerous overcrowding. Coverage of the event is found in 4 million pages of newspapers from the 18th and 19th centuries being made available online Tuesday by the British Library, in what head of newspapers Ed King calls “a digital Aladdin’s Cave” for researchers. The online archive is a partnership between the library and digital publishing firm Brightsolid, which has been scanning 8,000 pages a day from the library’s vast periodical archive for the past year and plans to digitize 40 million pages over the