fails:Symbol#casecmp with Symbol compares symbols without regard to case
fails:Symbol#casecmp with Symbol doesn't consider non-ascii characters equal that aren't
fails:Symbol#casecmp with Symbol doesn't do case mapping for non-ascii characters
fails:Symbol#casecmp returns nil if other is a String
fails:Symbol#casecmp returns nil if other is a Fixnum
fails:Symbol#casecmp returns nil if other is an object
