Use mrb_str_cat_lit() instead of mrb_str_cat_cstr() for string-literals.

Refactor kernel.c

delete obsolete macros (mrb_basic + mrb_object)

correctly validate symbol length

Over a year ago is not "soon" anymore. See:
88483fad
24366930

The comment didn't say why the length is reserved.
Using RITE_LV_NULL_MARK makes things a bit clearer.

This also fixes an off-by-one in mrb_check_intern().

Remove unused macro.

OutOfRange() is no longer used.

Fix error handlings for fprintf() and fputs() to file.

Unify and rename duplicated functions (noregexp() and regexp_check()).

Add prefix(mrb) to noregexp() and regexp_check().

add write barrier to env on pop call info poped. #2525

Add a missing space after ",".

Remove discareded NULL checks and use mrb_malloc() instead of mrb_realloc().