Fix three fatal errors when posting from 0.9.x:

Fix three fatal errors when posting from 0.9.x:
* OMB remote updates were trying to load nonexistent Laconica_OMB_Service_Consumer class -- fixed to StatusNet_OMB_Service_Consumer. Regression caused during libomb merge.
* Twitter processing was still being queued from core when no twitter plugin was present, which triggered an exception from UnqueueHandler; leftover code from before the plugin extraction.
* UnqueueHandler's exception caused a fatal error instead because it was missing the "new" keyword. Wouldn't have been seen when testing with the plugin enabled.