* vm_core.h: change semantics of opt_num and opt_table.
  `opt_num' was the number of optional parameters + 1.
  `opt_table' has "opt_num" entries.
  Change them to:
  `opt_num' is the number of optional parameters.
  `opt_talbe' has "opt_num + 1" entries.
  This change simplify parameter fitting logics.
* compile.c: catch up this change.
* iseq.c: ditto.
* proc.c: ditto.
* vm_args.c: ditto.



git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@48247 b2dd03c8-39d4-4d8f-98ff-823fe69b080e