test_module.rb: toplevel include

* test/ruby/test_module.rb (TestModule#test_include_toplevel): test
  for top level main.include.  based on a part of the patch by
  kyrylo at [GH-395].

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@43019 b2dd03c8-39d4-4d8f-98ff-823fe69b080e