mrb_sys_fail raises SystemCallError if we have it.
Merge branch 'master' into pr-systemcallerror
Merge branch 'master' into pr-systemcallerror
mrb_str_new2 -> mrb_str_new_cstr
set DATA_TYPE as soon as possible.
Add null check
Cut off eval_test from main
Merge pull request #1003 from kano4/pr-add-null-check

Add null check
Merge pull request #1004 from kano4/pr-cut-off-eval_test

Cut off eval_test from main
Merge pull request #996 from iij/pr-systemcallerror

mrb_sys_fail raises an instance of (subclass of) SystemCallError if we have it
Merge pull request #1000 from iij/pr-set-data-type-asap

DATA_TYPE must be set as soon as possible
Merge pull request #1002 from monaka/pr-extract-stack-zero-filling

Extract stack zero filling into new function.
Merge pull request #1001 from monaka/pr-add-type-check-in-mrb_str_to_cstr

Add the type check in mrb_str_to_cstr().
Define type mrb_bool. It is typedef-ed to _Bool on C99, unsigned int on MSVC.
It is safer than applying 1bit bit-fields to signed int.

For forward compatibility, you should substiture only 1 or 0 for the variable typed mrb_bool.