Fix some serious bugs in the way memcache was being used.  We were caching None values, because the value to be cached was computed *after* the memcache.add() call.  This was in the code ever since the use of memcache was introduced here, so it was never effective.  I also simplified the lookup in memcache_results to memcache_results.get(email), and decided to set the timeout to 5 minutes for all emails.  Most emails without nicknames will never actually get one assigned, because they are e.g. mailing lists or aliases for users who do their review under a different account.
Fix some serious bugs in the way memcache was being used.  We were
caching None values, because the value to be cached was computed
*after* the memcache.add() call.  This was in the code ever since the
use of memcache was introduced here, so it was never effective.  I
also simplified the lookup in memcache_results to
memcache_results.get(email), and decided to set the timeout to 5
minutes for all emails.  Most emails without nicknames will never
actually get one assigned, because they are e.g. mailing lists or
aliases for users who do their review under a different account.

I think this may obviate the need for the entity caching that Brad is
experimenting with in issue 2944.  I do notice that each Account is
loaded three times on a cache miss; but we should have many fewer
cache misses now...

ligthyear/quick-check,ligthyear/quick-check