For decades the Berlin district of Kreuzberg has been thought of as unconventional and nonconformist. For several months, it's also been accommodating several dozen refugees from Morocco, Senegal, Sudan and other African countries. But the immigrants from Africa haven't found a permanent home here. They are living in a disused school, tolerated by the authorities, eyed warily by residents, beset by the police. Because most are threatened with expulsion, some took refuge on the roof of the school. A report from Berlin.