Added test + fix for callbacks for destroy.

Change-Id: If25863ddeaf2a3a8744d19dcc13dddbe62b45e0b
Reviewed-on: http://review.couchbase.org/41660
Reviewed-by: Sergey Avseyev <sergey.avseyev@gmail.com>
Tested-by: Sergey Avseyev <sergey.avseyev@gmail.com>

lib/couchbase/active_model.rb

@@ -10,8 +10,8 @@ def self.included(base)
         include ::ActiveModel::Validations::Callbacks
         include ::ActiveModel::Dirty
 
-        define_model_callbacks :create, :update, :delete, :save, :initialize
-        [:save, :create, :update, :delete, :initialize].each do |meth|
+        define_model_callbacks :create, :update, :delete, :destroy, :save, :initialize
+        [:save, :create, :update, :delete, :destroy, :initialize].each do |meth|
           class_eval <<-EOC
             alias #{meth}_without_callbacks #{meth}
             def #{meth}(*args, &block)

test/test_active_model_integration.rb

@@ -70,7 +70,8 @@ def test_callbacks
       :after_initialize, :before_create, :around_create,
       :after_create, :before_delete, :around_delete,
       :after_delete, :before_save, :around_save, :after_save,
-      :before_update, :around_update, :after_update
+      :before_update, :around_update, :after_update,
+      :before_destroy, :around_destroy, :after_destroy
     ].each do |callback|
       assert ActiveObj.respond_to?(callback), "Model doesn't support callback: #{callback}"
     end