CamelOperation is now a subclass of GCancellable.  Instead of taking a
status update callback at creation time, it now emits a "status" signal
from an idle callback.

Several functions have been modified or removed:

   camel_operation_new()         No longer takes any arguments.
   camel_operation_unregister()  No longer takes any arguments
                                 (and never used it when it did).

   camel_operation_ref()         Gone. Use g_object_ref() instead.
   camel_operation_unref()       Gone. Use g_object_unref() instead.
   camel_operation_mute()        Gone. Disconnect your signal handler.