ostruct.rb: fix OpenStruct.allocate
* lib/ostruct.rb (OpenStruct.allocate): initialize an instance
variable directly, without calling `intialize` method which may
be overridden in a subclass. [ruby-core:80292] [Bug #13358]
ostruct.rb: improve fix for OpenStruct.allocate + #respond_to?
* lib/ostruct.rb (OpenStruct#respond_to_missing?): this makes
OpenStruct#respond_to? works on any OpenStruct instance,
just like Kernel#respond_to? does, without workarounds.
[ruby-core:80292] [Bug #13358]
merge revision(s) 58077,58229: [Backport #13358]
git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/branches/ruby_2_4@59407 b2dd03c8-39d4-4d8f-98ff-823fe69b080e