Writer.check_cached_data_okay_to_use(): fix comparing new commandline against old SFT header

 -this used to require exact string match, but SFT header
  can for some reason have the CLAs reordered
  (e.g. when ephemerides are involved)
 -introduce new helper function match_commandlines()
  and do proper unordered set comparison
 -also comment out log info about cff content checking,
  which wasn't actually implemented!