valgrind 3.9.0 on x86-64 reports a minor reduction in memory usage
when loading only RubyGems and RDoc by running: ruby -rrdoc -eexit

before: HEAP SUMMARY:
    in use at exit: 2,913,448 bytes in 27,394 blocks
  total heap usage: 48,362 allocs, 20,968 frees, 9,034,621 bytes alloc

after: HEAP SUMMARY:
    in use at exit: 2,880,056 bytes in 26,712 blocks
  total heap usage: 47,791 allocs, 21,079 frees, 9,046,507 bytes alloc

* class.c (struct clone_const_arg): adjust for id_table
  (clone_const): ditto
  (clone_const_i): ditto
  (rb_mod_init_copy): ditto
  (rb_singleton_class_clone_and_attach): ditto
  (rb_include_class_new): ditto
  (include_modules_at): ditto
* constant.h (rb_free_const_table): ditto
* gc.c (free_const_entry_i): ditto
  (rb_free_const_table): ditto
  (obj_memsize_of): ditto
  (mark_const_entry_i): ditto
  (mark_const_tbl): ditto
* internal.h (struct rb_classext_struct): ditto
* object.c (rb_mod_const_set): resolve class name on assignment
* variable.c (const_update): replace with const_tbl_update
  (const_tbl_update): new function
  (fc_i): adjust for id_table
  (find_class_path): ditto
  (autoload_const_set): st_update => const_tbl_update
  (rb_const_remove): adjust for id_table
  (sv_i): ditto
  (rb_local_constants_i): ditto
  (rb_local_constants): ditto
  (rb_mod_const_at): ditto
  (rb_mod_const_set): ditto
  (rb_const_lookup): ditto

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@53376 b2dd03c8-39d4-4d8f-98ff-823fe69b080e