Make `break`/`continue` behave as expected with `cleanup`.

[ta0kira]

For example:

cleanup {
  // cleanup 1
} in while (foo) {
  cleanup {
    // cleanup 2
  } in if (bar) {
    cleanup {
      // cleanup 3
    } in if (baz) {
      continue  // cleanup 3&2 (but not 1) should be executed here
    }
  }
}

[ta0kira]

Based on reasoning from #83, maybe break/continue should also be disallowed inside of cleanup. Even though the reasoning in #83 is specific to return interpretation, #84 proposes treating break/continue as semantically similar to return.