mruby/mruby — pull request #1762 by cubicdaiya (2014-02-27 16:36:29+00:00)
Title: fix SEGV bug for mrb_str_new

mrb_str_new causes seg-fault when 3rd argument is negative.

```c
/* example for reproducing */
mrb_value s = mrb_str_new(mrb, "string", -1);
```