merge revision(s) 40915: [Backport #8448]

	* variable.c (set_const_visibility): use rb_frame_this_func() instead
	  of rb_frame_callee() for getting the name of the called method

	* test/ruby/test_module.rb: add test for private_constant with no args


git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/branches/ruby_2_0_0@41064 b2dd03c8-39d4-4d8f-98ff-823fe69b080e