* ext/objspace/objspace.c: add a new method `reachable_objects_from_root'.
  ObjectSpace.reachable_objects_from_root returns all objects refered
  from root (called "root objects").
  This feature is for deep object analysis.
* test/objspace/test_objspace.rb: add a test.



git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@43301 b2dd03c8-39d4-4d8f-98ff-823fe69b080e
* NEWS: add a line into NEWS for last commit.



git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@43302 b2dd03c8-39d4-4d8f-98ff-823fe69b080e