simple front-end wrappers in Bugzilla.pm for use in the CGIs we have. r=bbaetz, joel; a=justdave. Adds a set of constants to the logout() API which allow specifying "how much" we should log out -- all sessions, the current session, or all sessions but the current one. Fixes callsites to use this new API; cleans and documents things a bit while we're at it. Part I in the great COOKIE apocalypse. git-svn-id: svn://10.0.0.236/trunk@154328 18797224-902f-48f8-a5cc-f745e15eee43