Require activesupport/all to more closely mirror a production Rails app.

ActiveSupport patches Kernel to add `class_eval` but this behavior wasn't
loaded in the test environment. This created a discrepancy between test
and prod, causing tests to fail that should have passed and vice versa.
Fully loading ActiveSupport makes the test environment more accurate.

elasticsearch-model/spec/spec_helper.rb

@@ -31,6 +31,10 @@
 require 'yaml'
 require 'active_record'
 
+# Load all of ActiveSupport to be sure of complete compatibility -
+# see https://github.com/elastic/elasticsearch-rails/pull/1075 for details
+require 'active_support/all'
+
 unless defined?(ELASTICSEARCH_URL)
   ELASTICSEARCH_URL = ENV['ELASTICSEARCH_URL'] || "localhost:#{(ENV['TEST_CLUSTER_PORT'] || 9200)}"
 end