eval.c: singleton class constants

* eval.c (rb_mod_s_constants): return its own constants for other
  than Module itself.  [ruby-core:59763] [Bug #9413]

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@44628 b2dd03c8-39d4-4d8f-98ff-823fe69b080e
* 2014-01-17

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@44629 b2dd03c8-39d4-4d8f-98ff-823fe69b080e