* cont.c (rb_fiber_reset_root_local_storage): add a new function to
	  restore rb_thread_t::local_storage.

	* cont.c (rb_obj_is_fiber): add a new function to tell finalizer to
	  prevent fibers from destroy.

	* gc.c (rb_objspace_call_finalizer): don't sweep fibers at finalizing
	  objspace.

	* internal.h (rb_fiber_reset_root_local_storage, rb_obj_is_fiber):
	  add prototypes.

	* vm.c (ruby_vm_destruct): reset main thread's local_storage before
	  free main thread. rb_thread_t::local_storage is replaced by fiber's
	  local storage when forked from fiber, and it should be already freed
	  when the fiber was destroyed.

	* test/ruby/test_fiber.rb (test_fork_from_fiber): add test for fork
	  from fiber.
	  when the fiber was destroyed. [ruby-core:41456] [Bug #5700]


git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/branches/ruby_1_9_3@34637 b2dd03c8-39d4-4d8f-98ff-823fe69b080e