Some reconfiguration failures are not caught as reconfig failures

[rhettg]

This is no good:

2011-06-22 11:34:04,635 tron.mcp ERROR Reconfiguration failed
Traceback (most recent call last):
  File "/usr/lib/python2.5/site-packages/tron/mcp.py", line 195, in live_reconfig
    self.load_config()
  File "/usr/lib/python2.5/site-packages/tron/mcp.py", line 208, in load_config
    configuration.apply(self)
  File "/usr/lib/python2.5/site-packages/tron/config.py", line 294, in apply
    self._apply_services(mcp)
  File "/usr/lib/python2.5/site-packages/tron/config.py", line 254, in _apply_services
    mcp.add_service(new_service)
  File "/usr/lib/python2.5/site-packages/tron/mcp.py", line 281, in add_service
    service.absorb_previous(prev_service)
  File "/usr/lib/python2.5/site-packages/tron/service.py", line 424, in absorb_previous
    self.build_instance()
  File "/usr/lib/python2.5/site-packages/tron/service.py", line 303, in build_instance
    node = self.node_pool.next_round_robin()
AttributeError: 'NoneType' object has no attribute 'next_round_robin'

Though the reconfiguration failed, this was not reported as an error or a failed reconfig (from tronfig's perspective)

[rhettg]

Fixed in 0.2.5