save returns _id as well

lib/mongo/collection.rb

@@ -77,6 +77,7 @@ module XGen
         def save(object)
           if id = object[:_id] || object['_id']
             repsert({:_id => id}, object)
+            id
           else
             insert(object)
           end

tests/test_db_api.rb

@@ -619,10 +619,11 @@ class DBAPITest < Test::Unit::TestCase
 
     a = {"hello" => "world"}
 
-    assert_kind_of ObjectID, @@coll.save(a)
+    id = @@coll.save(a)
+    assert_kind_of ObjectID, id
     assert_equal 1, @@coll.count
 
-    @@coll.save(@@coll.find_first)
+    assert_equal id, @@coll.save(@@coll.find_first)
     assert_equal 1, @@coll.count
 
     assert_equal "world", @@coll.find_first()["hello"]