"Much of what we think we know about African American history isn't completely true," says Betty DeRamus in the introduction to "Freedom by Any Means.""According to the usual story, slaves gained their freedom by running away, being freed by their owners, buying their way out of bondage or having someone else buy them. But how do we account for people like John Bowley, who bluffed his and his family's way to freedom, or Althea Lynch, whose cooking sprang her from jail? And what about all those who manage