Consolidates the logout code into Bugzilla::Auth::CGI, and provides
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.
Change code to work arround a perl < 5.8 leak when localising the tied
statement attributes. Also, clear the sql statestack compat stuff so that
the handles are really dead by the time we disconnect
r,a=justdave
