Removed STDERR pollution by API

Removed STDERR pollution by API
  * Accomplished this by introducing a GetErrorString() on most API
objects. When a method returns false, you can ignore it, parse the error
string to decide what to do next, prompt the user, make a sandwich,
whatever. But nothing should leak out to the console.
 * Internally the error messages are passed by a new BamException class.
This new exception should not cross the library boundary. The exception
should be caught "under the hood" and its what() string should be
(possibly formatted and) stored as the error string in one of the high-