[active_record] Fix loading for rails 3
[active_record] Fix loading for rails 3

tlunter/oboe-ruby,tlunter/oboe-ruby,appneta/ruby-traceview,boyang-li/oboe-ruby,tlunter/oboe-ruby,appneta/ruby-traceview,appneta/ruby-traceview,boyang-li/oboe-ruby,appneta/ruby-traceview,boyang-li/oboe-ruby,tlunter/oboe-ruby,boyang-li/oboe-ruby