make all Float objects frozen.
  [ruby-dev:46081] [ruby-trunk - Feature #6936]
  Most part of patch by NARUSE, Yui  <naruse@ruby-lang.org>.
* class.c (singleton_class_of): raise TypeError when
  trying to define a singleton method on Float objects.
* vm.c (vm_define_method): ditto.
* test/ruby/marshaltestlib.rb: catch up above changes.
* test/ruby/test_class.rb: ditto.
* test/test_pp.rb: ditto.



git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@37341 b2dd03c8-39d4-4d8f-98ff-823fe69b080e