send_message: Use a memcached for the UserProfile-by-id cache.

This cache should save 2 database queries whenever we send a private
message.  However, previously it was per-process (which meant it was
mostly useless) and also buggy (it never stored anything in the cache,
so that it was completely useless).  Switching this to our standard
memcached setup will address both problems.

(imported from commit 1d807f30704bccf28de33a80523488aedc58a9be)

zephyr/lib/actions.py

@@ -15,6 +15,7 @@ from django.utils import timezone
 from zephyr.lib.create_user import create_user
 from zephyr.lib.bulk_create import batch_bulk_create
 from zephyr.lib import bugdown
+from zephyr.lib.cache import cache_with_key, user_profile_by_id_cache_key
 
 import subprocess
 import simplejson
@@ -122,10 +123,8 @@ def log_message(message):
     if not message.sending_client.name.startswith("test:"):
         log_event(message.to_log_dict())
 
-user_hash = {}
+@cache_with_key(user_profile_by_id_cache_key)
 def get_user_profile_by_id(uid):
-    if uid in user_hash:
-        return user_hash[uid]
     return UserProfile.objects.select_related().get(id=uid)
 
 def do_send_message(message, rendered_content=None, no_log=False,