Refactor flo_finite_p()
Refactor fix_and()
Refactor fix_or()
Refactor fix_xor()
Merge pull request #2130 from suzukaze/refactor-numeric.c

Refactor numeric.c
check length before calling stack_copy(); based on a patch from @mirich; close #2129
Merge branch 'master' of github.com:mruby/mruby