Add ObsyncException
Add ObsyncException

This class has subclasses representing temporary and permanent
exceptions, as well as argument parsing errors. An instance of this
class can be created from a message or from another exception.

We always print out the type of exception on the last line of stderr,
right after the exception information.

Signed-off-by: Colin McCabe <7b35906f1d014e74a9dc8c913eb229119df647aa@dreamhost.com>

ajnelson/ceph,ajnelson/ceph,ajnelson/ceph,ajnelson/ceph,ajnelson/ceph,ajnelson/ceph