Wrap deferred.defer call for updating package counts in a try catch.

Ignore cases where we can't add the task to the task queue.

I tried running the test using test.py (after installing the prerequisites, but that did not work out for me (linux))
ricow@nobbo:/tmp/ricow-pub/pub-dartlang$ dev_appserver.py app 
INFO     2014-08-05 08:43:55,547 sdk_update_checker.py:242] Checking for updates to the SDK.
INFO     2014-08-05 08:43:55,821 sdk_update_checker.py:270] The SDK is up to date.
INFO     2014-08-05 08:43:55,840 api_server.py:171] Starting API server at: http://localhost:47834
INFO     2014-08-05 08:43:55,858 dispatcher.py:183] Starting module "default" running at: http://localhost:8080
INFO     2014-08-05 08:43:55,862 admin_server.py:117] Starting admin server at: http://localhost:8000
ERROR    2014-08-05 08:43:57,260 wsgi.py:262] 
Traceback (most recent call last):
  File "/tmp/app-engine/google_appengine/google/appengine/runtime/wsgi.py", line 239, in Handle
    handler = _config_handle.add_wsgi_middleware(self._LoadHandler())
  File "/tmp/app-engine/google_appengine/google/appengine/runtime/wsgi.py", line 298, in _LoadHandler
    handler, path, err = LoadObject(self._handler)
  File "/tmp/app-engine/google_appengine/google/appengine/runtime/wsgi.py", line 84, in LoadObject
    obj = __import__(path[0])
  File "/tmp/ricow-pub/pub-dartlang/app/pub_dartlang.py", line 17, in <module>
    import handlers
  File "/tmp/ricow-pub/pub-dartlang/app/handlers/__init__.py", line 21, in <module>
    from models.package_version import PackageVersion
  File "/tmp/ricow-pub/pub-dartlang/app/models/package_version.py", line 15, in <module>
    from handlers import cloud_storage
  File "/tmp/ricow-pub/pub-dartlang/app/handlers/cloud_storage.py", line 23, in <module>
    from models.private_key import PrivateKey
  File "/tmp/ricow-pub/pub-dartlang/app/models/private_key.py", line 10, in <module>
    from Crypto.Signature import PKCS1_v1_5
ImportError: No module named Signature
INFO     2014-08-05 08:43:57,273 module.py:642] default: "GET /_ah/warmup HTTP/1.1" 500 -

I also tried deploying a test version of the server, but it will not serve me packages.
Could one of you test this out or give me pointers besides the README on how to test this?
Add a comment here explaining why this is necessary and linking to the AppEngine issue in question.