Optional keyword argument Hash for rb_scan_args is Ruby 1.9.3 feature

see also r29214 of CRuby
rb_iter_break can't be test before 2.0

If you test it with extension library, it will cause SEGV and it needs
CRuby itself's fix. https://bugs.ruby-lang.org/issues/7896
rb_block_call and rb_obj_method are 1.8.7 feature
rb_syserr_fail and rb_make_backtrace are 1.9.3 feature
make sure to set the coderange

I doubt this spec because coderange is only a cache: it may be set as unknown.
1.8's Proc#inspect contains source location
'//' is C99 comment
Ignore deprecated warnings