pack.c: no nil.taint

* pack.c (pack_pack): nil is not taintable.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@47511 b2dd03c8-39d4-4d8f-98ff-823fe69b080e
variable.c: check index overflow

* variable.c (rb_ivar_set), vm_insnhelper.c (vm_setivar): check
  instance variable index overflow.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@47512 b2dd03c8-39d4-4d8f-98ff-823fe69b080e
compile.c: remove useless cast

* compile.c (rb_iseq_original_iseq): remove useless cast to fix
  compile error.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@47513 b2dd03c8-39d4-4d8f-98ff-823fe69b080e