disable features index since it uses a lot of ruby objects
Backport r39378 to fix at_exit hooks with rescue behavior.

```
Fri Feb 22 14:28:17 2013  Nobuyoshi Nakada  <nobu@ruby-lang.org>

	* eval_jump.c (rb_exec_end_proc): remember the latest exit status.
	  [ruby-core:43173][Bug #5218]
```

ref: http://bugs.ruby-lang.org/projects/ruby-193/repository/revisions/39378/diff
Merge branches 'p385/at-exit-hooks' and 'p385/disable-features-index' into github-p385