* io.c (rb_io_open_with_args): use RARRAY_CONST_PTR().

* io.c (rb_scan_open_args): use const qualifier for above.

* io.c (rb_open_file): ditto.

* io.c (rb_io_open_with_args): ditto.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@43581 b2dd03c8-39d4-4d8f-98ff-823fe69b080e