[ruby-core:18045] finalizers in 1.8 no longer run after gc_sweep()

This was brought up by Roger Pack in [ruby-talk:309757].

In 1.6, a finalizer would run immediately after the garbage collector  
collected an object. Now they are no longer run until the process  
terminates or an explicit GC.start is run:

$ cat final.rb
$finalizer_proc = proc do |obj_id| puts "#{obj_id} finalized" end

def a() b end
def b() c end
def c() d end
def d() e end
def e() f end
def f() g end
def g() h end
def h() i end
def i() j end
def j() k end
def k() make_obj end

def make_obj
  o = Object.new
  ObjectSpace.define_finalizer o, $finalizer_proc
  o.__id__
end

obj_id = a

puts "#{obj_id} created"

a = []
s = 'a'

begin
  loop do
    ObjectSpace._id2ref obj_id
    a << s.succ!
    print "#{s}\r"
  end
rescue RangeError
  puts
  puts "#{obj_id} collected"
end

$ ruby -v final.rb
ruby 1.8.6 (2008-03-03 patchlevel 114) [universal-darwin9.0]
81660 created
avr
81660 collected
81660 finalized
$ ruby16 -v final.rb
ruby 1.6.8 (2005-09-21) [i386-darwin9.4.0]
1117686 created
1117686 finalized
omu
1117686 collected
$

I would expect the finalized line to print before the collected line  
at all times.  This is no longer true.

Running the finalizers in gc_sweep() was removed in r7090.  The  
following patch restores the 1.6 behavior, but I'm unsure if it re- 
introduce some problem from [ruby-dev:24536].

Index: gc.c
===================================================================
--- gc.c	(revision 18230)
+++ gc.c	(working copy)
@@ -1196,7 +1196,7 @@ gc_sweep()

      /* clear finalization list */
      if (final_list) {
-	deferred_final_list = final_list;
+	finalize_list(final_list);
  	return;
      }
      free_unused_heaps();