47 - added progress support to obsolescence markers pushing

    47 

    48 - added multiple output during obsolescence marrkers exchange

    48 - improvement to obsolescence marker exchange:

    49 - record parent of pruned parent at prune time

    49   - record parent of pruned parent at prune time

    50 - only push markers relevant to pushed subset

    50   - added progress when pushing obsmarkers

    51 - only pull markers relevant to pulled subset (if server support)

    51   - added multiple output during obsolescence markers exchange

    52 - added progress support for push and pull of markers over wire protocol

    52   - only push markers relevant to pushed subset

    53   - add a new experimental way to exchange marker (when server support):

    54     - added progress when pulling obsmarkers

    55     - only pull markers relevant to pulled subset

    56     - avoid exchanging common markers in some case