tor/changes/feature18329

  o Minor features:
    - Bridge relays can now set the BridgeDistribution config option to
      add a "bridge-distribution-request" line to their bridge descriptor,
      which tells BridgeDB how they'd like their bridge address to be
      given out. (Note that as of Oct 2017, BridgeDB does not yet implement
      this feature.) As a side benefit, this feature provides a way
      to distinguish bridge descriptors from non-bridge descriptors.
      Implements tickets 18329.