Implement stricter control of criteria operators
Implement stricter control of criteria operators

Solves issue #944
josh64x2/vienna-rss,barijaona/vienna-rss,barijaona/vienna-rss,lapcat/vienna-rss,ViennaRSS/vienna-rss,ViennaRSS/vienna-rss,ViennaRSS/vienna-rss,ViennaRSS/vienna-rss,barijaona/vienna-rss,lapcat/vienna-rss,Eitot/vienna-rss,Eitot/vienna-rss,Eitot/vienna-rss,lapcat/vienna-rss,josh64x2/vienna-rss,ViennaRSS/vienna-rss,barijaona/vienna-rss,Eitot/vienna-rss,josh64x2/vienna-rss,barijaona/vienna-rss,josh64x2/vienna-rss,josh64x2/vienna-rss,lapcat/vienna-rss