title: Debug/reproduce EXC_BAD_ACCESS crash in CA::release_objects
body: <p>I use Crashlytics to track crashes and I am seeing some crashes with the stack trace below:</p>
  
  <p>Crashed: com.apple.main-thread
  EXC_BAD_ACCESS KERN_INVALID_ADDRESS at 0xf8560b1c</p>
  
  <pre><code>Thread : Crashed: com.apple.main-thread
  0  libobjc.A.dylib                0x37a20b66 objc_msgSend + 5
  1  CoreFoundation                 0x2d5f8e8d CFRelease + 560
  2  QuartzCore                     0x2fad2965 CA::release_objects(X::List&lt;void const*&gt;*) + 16
  3  QuartzCore                     0x2fad7dcf -[CAAnimation dealloc] + 54
  4  libobjc.A.dylib                0x37a30b0b objc_object::sidetable_release(bool) + 174
  5  CoreFoundation                 0x2d5f8e8d CFRelease + 560
  6  QuartzCore                     0x2fada419 CA::Layer::run_animation_callbacks(void*) + 240
  7  libdispatch.dylib              0x37f0a0af _dispatch_client_callout + 22
  8  libdispatch.dylib              0x37f0c9a9 _dispatch_main_queue_callback_4CF + 268
  9  CoreFoundation                 0x2d6935b1 __CFRUNLOOP_IS_SERVICING_THE_MAIN_DISPATCH_QUEUE__ + 8
  10 CoreFoundation                 0x2d691e7d __CFRunLoopRun + 1308
  11 CoreFoundation                 0x2d5fc471 CFRunLoopRunSpecific + 524
  12 CoreFoundation                 0x2d5fc253 CFRunLoopRunInMode + 106
  13 GraphicsServices               0x323362eb GSEventRunModal + 138
  14 UIKit                          0x2feb1845 UIApplicationMain + 1136
  </code></pre>
  
  <p>It looks like CFRelease is being called on some object twice. The problem is I have no idea which animation is causing the crash. The logs aren't very helpful as the crash happens in different places. How do I go about debugging/reproducing this crash or at the very least logging something so that I know what object is being released twice.</p>