Add null check after mrb_realloc for array
Remove warning for regexp
Merge pull request #954 from carsonmcdonald/arrcrashfix

Add null check after mrb_realloc for array
Merge pull request #957 from mattn/no_ambiguous

Remove warning for regexp
Cut off mrb_irep_free from mrb_close; based on a patch from @matsumoto-r; close #951