rem: QString operator()( const GpgME::Key & key ) { return key.subkey(0).fingerprint();
add: bool operator()( const GpgME::Key & key ) const { return key.keyListMode() & GpgME::Context::Validate ;
context:     QString operator()( const GpgME::Key & key ) {      return key.subkey(0).fingerprint();    }