vm_core.h: preserve thread ordering

I'm hesitant to consider this as spec, but this causes a
user-visible change which could break user code.

* vm_core.h (rb_vm_living_threads_insert): preserve order
  [Bug #10660] [ruby-core:67154] [ruby-core:67159]

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@49036 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

ChangeLog

@@ -1,3 +1,8 @@
+Sat Dec 27 15:08:27 2014  Eric Wong  <e@80x24.org>
+
+	* vm_core.h (rb_vm_living_threads_insert): preserve order
+	  [Bug #10660] [ruby-core:67154] [ruby-core:67159]
+
 Sat Dec 27 13:08:20 2014  SHIBATA Hiroshi  <shibata.hiroshi@gmail.com>
 
 	* ext/socket/socket.c: improved document for YARD doc.

vm_core.h

@@ -975,7 +975,7 @@ rb_vm_living_threads_init(rb_vm_t *vm)
 static inline void
 rb_vm_living_threads_insert(rb_vm_t *vm, rb_thread_t *th)
 {
-    list_add(&vm->living_threads, &th->vmlt_node);
+    list_add_tail(&vm->living_threads, &th->vmlt_node);
     vm->living_thread_num++;
 }