* include/ruby/ruby.h: constify RArray::as::ary and RArray::heap::ptr.
  Use RARRAY_ASET() or RARRAY_PTR_USE() to modify Array objects.
* array.c, gc.c: catch up above changes.



git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@41537 b2dd03c8-39d4-4d8f-98ff-823fe69b080e