LONDON (Reuters) - British bank Barclays said first-quarter profit fell a quarter from a year ago, as a hefty bill for the cost of a restructuring plan by its new chief executive offset a solid performance by its investment bank. Adjusted pretax profit for the three months through March dropped to 1.79 billion pounds ($2.7 billion) from 2.4 billion a year ago, just below a mean forecast of 1.85 billion from analysts polled by the company. ...