load.c: reduce indexes arrays

* load.c (features_index_add_single, rb_feature_p): store single index
  as Fixnum to reduce the number of arrays for the indexes.  based on
  the patch by tmm1 (Aman Gupta) in [ruby-core:53216] [Bug #8048].

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@39644 b2dd03c8-39d4-4d8f-98ff-823fe69b080e
load.c: move loop invariant condition

* load.c (rb_feature_p): move this_feature_index condition which is
  loop invariant.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@39645 b2dd03c8-39d4-4d8f-98ff-823fe69b080e
load.c: hide internal objects

* load.c (rb_construct_expanded_load_path, Init_load): hide internal
  objects, expanded_load_path, {load_path,loaded_features}_snapshot,
  and loaded_features_index in the VM, and ruby_dln_librefs.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@39646 b2dd03c8-39d4-4d8f-98ff-823fe69b080e
fix commit miss

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@39647 b2dd03c8-39d4-4d8f-98ff-823fe69b080e
configure.in: note to remove a hack

* configure.in (rm): note to remove this hack when AC_PREREQ(2.70) or
  later.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@39648 b2dd03c8-39d4-4d8f-98ff-823fe69b080e
* io.c: Fix rdoc typo [Github fixes #256]

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@39649 b2dd03c8-39d4-4d8f-98ff-823fe69b080e