Timezone modified Calendar equivalence error

Imported from http://bugzilla.roxen.com/bugzilla/show_bug.cgi?id=1884

Reported by Fredrik Noring, Roxen Internet Software noring@roxen.com

Both equal calls are supposed to return 1:

  Pike v7.2 release 75 running Hilfe v2.0 (Incremental Pike Frontend)
  > string fmt = "%dT%h:%m:%s", tm = "19980717T14:08:55";
  Result: "%dT%h:%m:%s"
  Result: "19980717T14:08:55"
  > equal(Calendar.ISO.parse(fmt, tm)->set_timezone("UTC"),
  >>      Calendar.ISO.parse(fmt, tm)->set_timezone("UTC"));
  Result: 1
  > equal(Calendar.ISO.set_timezone("UTC")->parse(fmt, tm),
  >>      Calendar.ISO.set_timezone("UTC")->parse(fmt, tm));
  Result: 0