Added active_record_query_trace

This can be used to track down where queries originate from, regardless
of whether they're caused by N+1 problems or not. This can be enabled by
setting the environment variable ENABLE_QUERY_TRACE to a non-empty value
(e.g. "true").

Gemfile

@@ -225,6 +225,7 @@ group :development do
   gem 'rack-mini-profiler', '~> 0.9.0', require: false
   gem 'rerun', '~> 0.10.0'
   gem 'bullet', require: false
+  gem 'active_record_query_trace', require: false
   # Better errors handler
   gem 'better_errors', '~> 1.0.1'

Gemfile.lock

@@ -17,6 +17,7 @@ GEM
       activesupport (= 4.1.12)
       builder (~> 3.1)
       erubis (~> 2.7.0)
+    active_record_query_trace (1.5)
     activemodel (4.1.12)
       activesupport (= 4.1.12)
       builder (~> 3.1)
@@ -788,6 +789,7 @@ PLATFORMS
 DEPENDENCIES
   RedCloth (~> 4.2.9)
   ace-rails-ap (~> 2.0.1)
+  active_record_query_trace
   activerecord-deprecated_finders (~> 1.0.3)
   activerecord-session_store (~> 0.1.0)
   acts-as-taggable-on (~> 3.4)

config/initializers/active_record_query_trace.rb

+if ENV['ENABLE_QUERY_TRACE']
+  require 'active_record_query_trace'
+
+  ActiveRecordQueryTrace.enabled = 'true'
+end