Clean up uniques when deleting

A bug in the test where the key "unique" was used 
instead of "uniques" meant the test 
"removes the previous index when deleting" was
passing when it was in fact failing. Model.delete 
now mirrors Model.save in how it cleans up indexes
and uniques.

lib/ohm.rb

@@ -1345,7 +1345,8 @@ def delete
       transaction do |t|
         _uniques = nil
         _indices = nil
-        existing = nil
+        existing_indices = nil
+        existing_uniques = nil
 
         t.watch(*_unique_keys)
 
@@ -1354,15 +1355,17 @@ def delete
         t.watch(key[:_uniques]) if model.uniques.any?
 
         t.read do
-          existing = _read_attributes(model.indices) if model.indices.any?
+          existing_indices = _read_attributes(model.indices) if model.indices.any?
+          existing_uniques = _read_attributes(model.uniques) if model.uniques.any?
           _uniques = db.hgetall(key[:_uniques])
           _indices = db.smembers(key[:_indices])
         end
 
         t.write do
           _delete_uniques(_uniques)
           _delete_indices(_indices)
-          _delete_existing_indices(existing)
+          _delete_existing_uniques(existing_uniques)
+          _delete_existing_indices(existing_indices)
           model.collections.each { |e| db.del(key[e]) }
           db.srem(model.key[:all], id)
           db.del(key[:counters])

test/uniques.rb

@@ -64,15 +64,15 @@ def provider
   u.update(:email => "d@d.com")
 
   assert_equal nil, User.with(:email, "c@c.com")
-  assert_equal nil, User.key[:unique][:email].hget("c@c.com")
+  assert_equal nil, User.key[:uniques][:email].hget("c@c.com")
   assert_equal u, User.with(:email, "d@d.com")
 end
 
 test "removes the previous index when deleting" do |u|
   u.delete
 
   assert_equal nil, User.with(:email, "a@a.com")
-  assert_equal nil, User.key[:unique][:email].hget("a@a.com")
+  assert_equal nil, User.key[:uniques][:email].hget("a@a.com")
 end
 
 test "unique virtual attribute" do