Fix uninitialized variable in hex_to_str().

 * In the worst case cause a Segmentation Fault
   * VM read the irep is illegal irep code.

 * Because, since it's not NULL terminated in the process of strncpy(3),
   it may strtol(3) doesn't return the correct value.
moved to iij/mruby-rpm-spec
test/t/file.rb update
refactoring: mrb_gv_alias_name_check
strcmp -> strncmp; mrbtest verbose mode check