* FreeBSD returns errno 31 (EMLINK, Too many links),
  not 40 (ELOOP, Too many levels of symbolic links)
* (`mysqlbinlog|mysql`) was just crazy, why did it ever work?
* socket_ipv6.inc check (that checked whether ipv6 is supported)
  only worked correctly when ipv6 was supported
* perfschema.socket_summary_by_instance was changing global variables
  and then skip-ing the test (because on missing ipv6)