Stop using ^ for snapshots
    
    In previous scheme, carets were used for both snapshots and any
    "post-releases", i.e. non-numerical upstream bugfix versions.
    But to make sure that snapshots based from the initial release sort
    earlier than a subsequent post-release, the snapshot needed to start
    with a double caret. This was rather complex and people didn't like it.
    
    It turns out to be unnecessary for two reasons:
    - a normal dot is actually appropriate for post-release versions.
      It already sorts later than the release, so we don't need to do anything
      special.
    - I looked over list of all packages returned by
      'dnf list --releasever=rawhide --disablerepo=\* --enablerepo=fedora-source',
      and there's just a handful of packages with non-sorting versions.
      I think that fancy version schemes were more popular in the past,
      and nowadays semver and ubuntu-style date-based versions are much
      more popular. So any fancy scheme that we come up would be used for
      maybe a few packages out of 20k+ source packages currently in Fedora.
      We can handle those few special cases using snaphot-like date-based
      versions, and keep the general case simpler.
    
    In the new sheme is that ^ is only used for non-release snapshots.