This is a function to decode PHP session data. Normally this data
appears, for the current user, magically parsed for you, in $_SESSION.
But sometimes you need to access that data from some other service,
that might not even be the current user.

There are some functions in the php.net page about this, but as of
August 2011 none of them tries really hard to avoid escaping issues.
This isn't rigorously tested but seems to work okay. It turns out
I did not need this for my project but maybe it will be helpful as
a starting point to someone else.

-- Neil Kandalgaonkar <neilk@brevity.org>