Home prices are increasing, new building permits are on the rise, and foreclosures have dropped, offering the strongest evidence yet of a sustained recovery in the Greater Boston housing market, according to report to be released Thursday…“We think we’ve turned the corner,” said Barry Bluestone, the director of the Kitty and Michael Dukakis Center for Urban and Regional Policy at Northeastern University and lead author of the study. But he added, “The economy is leaving housing affordability behind.”