mruby/mruby — pull request #1427 by Fleurer (2013-08-01 10:32:02+00:00)
Title: remove the minor GC introduced in clear_all_old(), and introduce prepare_major_gc()

1)

```
if (is_major_gc(mrb)) {
incremental_gc_until(mrb, GC_STATE_NONE);
}
```

this snippet from `clear_all_old()` is in fact triggering a MINOR gc if it's `is_major_gc()`. is there any reason on this?

2) `clear_all_old()` is pretty precise on what it does, but `prepare_major_gc()` is more descriptive on what's its role