- need to detect zero division error
- support floating point number argument (as `%`)

This reverts commit 3738d62a.
The change changed the behavior with floating point numbers.

`mrb_as_int` implicitly converts the value into the integer, but those
methods are defined for Integer class so that the value should always be
integers.

Use `mrb_fixnum_value()` only when you are absolutely sure that the
value is within `Fixnum` range, i.e. 31 bits signed integer at least.

The `Fixnum` class is no longer provided by `mruby`.

For example, `while false; ...; end` should be removed.

It rescans `s->iseq` so that peephole optimizer can take multiple
previous instructions for constant folding, etc.

`while` and `until` generates in `cond` `jmpif` `body` `jmp` order.
It used to be in `jmp` `body` `cond` `jmpif` order.

- `pc0`: `next` destination
- `pc1`: `redo` destination (renamed from `pc2`)
- `pc3`: `break` destination (renamed from `pc3`)

old `pc1` was unused so removed.

```ruby
p ((while true; p 1; break; end))
```

should print `1 nil` but was `1`.

pre-commit autoupdate

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Also, now too big capture group index just gives `nil`, not error.