bugzilla: stop trying to cache setup across hook invocation In the context of standalone Hg receiving a set of incoming changes, it makes sense for the Bugzilla module to cache basic setup to avoid reconnecting to Bugzilla for each change. After processing the changes, Hg will exit and so the connection is short-lived. But this doesn't work too well when used from a long-lived environment such as hgweb or Kallithea where, for example, the connection can time out. So take the simple approach, abandon the cache and do the basic setup on each call. This fixes current problems with Kallithea.