use fedfind get_package_nvras, check packages are newer
    
    This improves the 'should we create an event for a nightly when
    it's been between 3 and 14 days since the last event' logic to
    check that the significant packages are *newer* than they were
    in the current event's compose, not just that they're different.
    This should avoid a possible case where we have a blocker/FE
    fix to one of the 'significant' packages in a candidate compose
    and it doesn't get pushed stable, then we don't create a new
    candidate compose for 3 days; on the fourth day we might wind
    up creating an event for that day's nightly because it contains
    an older version of the package, which we really don't want.
    
    Note, this doesn't cover two other possible cases:
    
    1) a 'significant' package is newer in the nightly, but another
       package is older
    2) > 14 days but nightly is still older than candidate
    
    it does fix the most obviously bad case, though. To enable this,
    fedfind was changed to return N(E)VRAs, so we can use hawkey
    to do the comparisons and be sure they're done properly.