object.c: fix typo

* object.c (rb_mod_const_get): fix typo.  should use SYM2ID() not
  ID2SYM().

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@44192 b2dd03c8-39d4-4d8f-98ff-823fe69b080e
object.c: remove unnecessary assignment

* object.c (rb_mod_const_get): remove unnecessary assignment and
  set path together.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@44193 b2dd03c8-39d4-4d8f-98ff-823fe69b080e
object.c: nested path const_defined?

* object.c (rb_mod_const_defined): support nested class path as
  well as const_get.  [Feature #7414]

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@44194 b2dd03c8-39d4-4d8f-98ff-823fe69b080e