adding code and spec to fix blindness to callbacks that return false …

…during updates

lib/mongoid/persistence/update.rb

@@ -50,11 +50,12 @@ def persist
                 child.move_changes
                 child.new_record = false if child.new_record?
               end
+              true
             else
               return false
             end
           end
-        end; true
+        end
       end
 
       protected

spec/unit/mongoid/persistence/update_spec.rb

@@ -133,6 +133,16 @@ def tree_set_expectation
           update.persist.should == true
         end
       end
+
+      context "when before_save callback returns false" do
+        before do
+          Patient.set_callback :save, :before, lambda { |r| return false }
+        end
+
+        it "returns false" do
+          document.save.should == false
+        end
+      end
 
       context "when the document is embedded" do