o Minor bugfixes (bridge clients, bootstrap):
    - Retry directory downloads when we get our first bridge descriptor
      during bootstrap or while reconnecting to the network. Keep retrying
      every time we get a bridge descriptor, until we have a reachable bridge.
      Fixes bug 24367; bugfix on 0.2.0.3-alpha.
    - Stop delaying bridge descriptor fetches when we have cached bridge
      descriptors. Instead, only delay bridge descriptor fetches when we
      have at least one reachable bridge.
      Fixes bug 24367; bugfix on 0.2.0.3-alpha.
    - Stop delaying directory fetches when we have cached bridge descriptors.
      Instead, only delay bridge descriptor fetches when all our bridges are
      definitely unreachable.
      Fixes bug 24367; bugfix on 0.2.0.3-alpha.