Found and fixed code deserialization bug.

lib/mongo/util/bson.rb

@@ -87,7 +87,7 @@ class BSON
     while @buf.more?
       type = @buf.get
       case type
-      when STRING
+      when STRING, CODE
         key = deserialize_element_name(@buf)
         doc[key] = deserialize_string_data(@buf)
       when NUMBER

tests/test_bson.rb

@@ -10,7 +10,13 @@ class BSONTest < Test::Unit::TestCase
   end
 
   def test_object_encoding
-    doc = {'doc' => {'age' => 41.2, 'name' => 'Spongebob'}}
+    doc = {'doc' => {'age' => 42, 'name' => 'Spongebob', 'shoe_size' => 9.5}}
+    @b.serialize(doc)
+    assert_equal doc, @b.deserialize
+  end
+
+  def test_code_encoding
+    doc = {'$where' => 'this.a.b < this.b'}
     @b.serialize(doc)
     assert_equal doc, @b.deserialize
   end