Fix origin iclass pointer for modules

If a module has an origin, and that module is included in another
module or class, previously the iclass created for the module had
an origin pointer to the module's origin instead of the iclass's
origin.

Setting the origin pointer correctly requires using a stack, since
the origin iclass is not created until after the iclass itself.
Use a hidden ruby array to implement that stack.

Correctly assigning the origin pointers in the iclass caused a
use-after-free in GC.  If a module with an origin is included
in a class, the iclass shares a method table with the module
and the iclass origin shares a method table with module origin.

Mark iclass origin with a flag that notes that even though the
iclass is an origin, it shares a method table, so the method table
should not be garbage collected.  The shared method table will be
garbage collected when the module origin is garbage collected.
I've tested that this does not introduce a memory leak.

This also includes a fix for Module#included_modules to skip
iclasses with origins.

Fixes [Bug #16736]

test/ruby/test_module.rb

@@ -479,6 +479,28 @@ class TestModule < Test::Unit::TestCase
     assert_raise(ArgumentError) { Module.new { include } }
   end
 
+  def test_gc_prepend_chain
+    assert_separately([], <<-EOS)
+      10000.times { |i|
+        m1 = Module.new do
+          def foo; end
+        end
+        m2 = Module.new do
+          prepend m1
+          def bar; end
+        end
+        m3 = Module.new do
+          def baz; end
+          prepend m2
+        end
+        Class.new do
+          prepend m3
+        end
+      }
+      GC.start
+    EOS
+  end
+
   def test_include_into_module_already_included
     c = Class.new{def foo; [:c] end}
     modules = lambda do ||
@@ -540,6 +562,16 @@ class TestModule < Test::Unit::TestCase
     assert_equal([Comparable, Kernel], String.included_modules - mixins)
   end
 
+  def test_included_modules_with_prepend
+    m1 = Module.new
+    m2 = Module.new
+    m3 = Module.new
+
+    m2.prepend m1
+    m3.include m2
+    assert_equal([m1, m2], m3.included_modules)
+  end
+
   def test_instance_methods
     assert_equal([:user, :user2], User.instance_methods(false).sort)
     assert_equal([:user, :user2, :mixin].sort, User.instance_methods(true).sort)
@@ -2043,6 +2075,33 @@ class TestModule < Test::Unit::TestCase
     assert_include(im, mixin, bug8025)
   end
 
+  def test_prepended_module_with_super_and_alias
+    bug16736 = '[Bug #16736]'
+
+    a = labeled_class("A") do
+      def m; "A"; end
+    end
+    m = labeled_module("M") do
+      prepend Module.new
+
+      def self.included(base)
+        base.alias_method :base_m, :m
+      end
+
+      def m
+        super + "M"
+      end
+
+      def m2
+        base_m
+      end
+    end
+    b = labeled_class("B", a) do
+      include m
+    end
+    assert_equal("AM", b.new.m2, bug16736)
+  end
+
   def test_prepend_super_in_alias
     bug7842 = '[Bug #7842]'