replay: always fetch the entire first revision The entire revision is fetched using the just-added get_revision() wrapper. Essentially, this allows us to begin a conversion with a non-zero start revision. As an extra safety feature, this mode is *always* used for the very first revision, even if no start revision is specified. For most repositories, this shouldn't matter; the entire revision will be fetched regardless. However, there are repositories that currently `confuse' us, such as bzr-svn conversions, and where this is an improvement.