This fixes #73

Hi @zzzeek would you mind taking a look on the api? I also tested dogpile tests + the ones of concurrency and everything seems to be working.

OK, you uncommented the ones that were failing a long time ago? that's great. if you release this I can look into re-enabling those tests on my end.

@zzzeek Yes, I removed all the skips and they seem to be working

@zzzeek this should be working now

confirmed this repairs normal test coverage, thanks very much! testing out the previously skipped tests as a separate change.

still seeing a failure for the "concurrency" tests: https://jenkins.sqlalchemy.org/job/dogpile_gerrit/59/backend=memcached,pyv=py36/testReport/junit/tests.cache.test_memcached_backend/BMemcachedDistributedWithTimeoutTest/test_threaded_dogpile/ . These tests are quite crazy so aren't that great to figure out what might be going on, unfortunately.

strange, they worked on a clean docker environment. I will make some changes and try to figure it out.