Failing test showing the lack of a new session on successful auth

This only occurs when Apache::Session::File is RT's session handler
since it revivifies the session.  However, core RT's practice is to
always instantiate a new session on successful auth, and this extension
should follow suit.
Instantiate a new session upon successful authentication

This matches core RT's handling and ensures a fresh, clean session for
the newly logged in user.  Resolves a problem where old sessions (and
cached data) are reused under Apache::Session::File.
Continue to support the next page after login

Instantiating a new session during auth now requires grabbing the next
page key before we kill the old session.
change indents to fit reasonable screen size
convert comments into POD
move config docs into config
move docs from comments into POD
Additional updates to docs
typo in etc/RT_SiteConfig.pm
delete lies in d_filter description
mention AD specific d_filter, not bad example
Merge branch 'session-reuse'
Explain session handling changes in ChangeLog
Merge branch 'docs-improvements'