MONGOID-5214 Make unscoped clear current scope or document that it does not (#5478)

Author: neilshweky

lib/mongoid/scopable.rb

@@ -175,7 +175,9 @@ def scoped(options = nil)
       def unscoped
         if block_given?
           without_default_scope do
-            yield(self)
+            with_scope(nil) do
+              yield(self)
+            end
           end
         else
           queryable.unscoped

spec/mongoid/scopable_spec.rb

@@ -1265,8 +1265,6 @@ class << Band
       let(:c1) { Band.where(active: true) }
 
       it 'restores previous scope' do
-        pending 'MONGOID-5214'
-
         Band.with_scope(c1) do |crit|
           Band.unscoped do |crit2|
             Mongoid::Threaded.current_scope(Band).should be nil