auth_to_local should allow array values

[riton]

As described in man krb5.conf, such configuration should be possible:

[realms]
ATHENA.MIT.EDU = {
  auth_to_local = RULE:[2:$1](johndoe)s/^.*$/guest/
  auth_to_local = RULE:[2:$1;$2](^.*;admin$)s/;admin$//
  auth_to_local = RULE:[2:$2](^.*;root)s/^.*$/root/
  auto_to_local = DEFAULT
}

Currently, such configuration is impossible since auth_to_local does not support array values.