* ext/objspace/object_tracing.c: fix a bug reported at
  "[ruby-core:55182] [ruby-trunk - Bug #8456][Open] Sugfault in Ruby Head"
  Care about the case TracePoint#path #=> `nil'.
* ext/objspace/object_tracing.c: add two new methods:
* ObjectSpace.allocation_class_path(o)
* ObjectSpace.allocation_method_id(o)
  They are not useful for Object.new because they are always
  "Class" and :new.
  To trace more useful information, we need to maintain call-tree
  using call/return hooks, which is implemented by
  ll-prof <http://sunagae.net/wiki/doku.php?id=software:llprof>
* test/objspace/test_objspace.rb: add a test.



git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@40974 b2dd03c8-39d4-4d8f-98ff-823fe69b080e