(Reuters) - Homebuilder Barratt Developments on Wednesday posted an increase in first-half pretax profit as demand for lower-priced homes surged, and said it would pay a special dividend of 175 million pounds next year. Britain's largest homebuilder has been trying to cut costs by changing the design of the houses and reducing exposure to central London by focusing on outer parts of the city. The company said its pretax profit rose 3.7% to 423 million pounds for the six months ended Dec. 31...