Ruby

check modifcation whil ar->st

• delete ar_try_convert but use ar_force_convert_table
  to make program simple.
• ar_force_convert_table checks hash modification while
  calling #hash method with the following strategy:

1. copy keys (and vals) of ar_table
2. calc hashes from keys
3. check copied keys and hash's keys. if not matched, repeat from 1

fix [Bug #20050]