Report the correct value of nil.id in the exception message

as different ruby implementations may have different values,
for example Rubinius returns 53 for nil.id.

[#6444 state:resolved]

activesupport/lib/active_support/whiny_nil.rb

@@ -37,7 +37,7 @@ class NilClass
 
   # Raises a RuntimeError when you attempt to call +id+ on +nil+.
   def id
-    raise RuntimeError, "Called id for nil, which would mistakenly be 4 -- if you really wanted the id of nil, use object_id", caller
+    raise RuntimeError, "Called id for nil, which would mistakenly be #{object_id} -- if you really wanted the id of nil, use object_id", caller
   end
 
   private

activesupport/test/whiny_nil_test.rb

@@ -33,9 +33,11 @@ class WhinyNilTest < Test::Unit::TestCase
   end
 
   def test_id
+    nil.stubs(:object_id).returns(999)
     nil.id
   rescue RuntimeError => nme
     assert_no_match(/nil:NilClass/, nme.message)
+    assert_match(/999/, nme.message)
   end
 
   def test_no_to_ary_coercion