* gc.c: add support to estimate increase of oldspace memory usage.
  This is another approach to solve an issue discussed at r43530.
  This feature is diabled as default.
  This feature measures an increment of memory consuption by oldgen
  objects. It measures memory consumption for each objects when
  the object is promoted. However, measurement of memory consumption
  is not accurate now. So that this measurement is `estimation'.
  To implement this feature, move memsize_of() function from
  ext/objspace/objspace.c and expose rb_obj_memsize_of().
  Some memsize() functions for T_DATA (T_TYPEDDATA) have problem to
  measure memory size, so that we ignores T_DATA objects now.
  For example, some functions skip NULL check for pointer.
  The macro RGENGC_ESTIMATE_OLDSPACE enables/disables this feature,
  and turned off as default.
  We need to compare 3gen GC and this feature carefully.
  (it is possible to enable both feature)
  We need a help to compare them.
* internal.h: expose rb_obj_memsize_of().
* ext/objspace/objspace.c: use rb_obj_memsize_of() function.
* cont.c (fiber_memsize): fix to check NULL.
* variable.c (autoload_memsize): ditto.
* vm.c (vm_memsize): ditto.



git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@43532 b2dd03c8-39d4-4d8f-98ff-823fe69b080e
fix typos in ChangeLog.



git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@43533 b2dd03c8-39d4-4d8f-98ff-823fe69b080e