rename singleton_class to single_class and misc

was clashing with real ruby method name
also many superclass mismatch fixes
some misc

test/elf/test_somethingelse.rb

@@ -6,7 +6,7 @@ module Elf
     def test_string_put
       hello = "Hello World!\n"
       input = "return '#{hello}'.putstring"
-      preload = "class Word;def putstring;X.putstring;end;end;"
+      preload = "class Word < Data8;def putstring;X.putstring;end;end;"
       @stdout = hello
       @exit_code = hello.length
       check preload + as_main(input), "hello"