Non-persistent session support added to gaesessions

[Concrete]

I added support for non-persistent sessions to gaesessions v1.06. A
zip file with the code can be downloaded from the URL below. Of
course I'd like to see this merged into the trunk code so I don't have
to merge every time I download an update but no worries if this isn't
feasible. If you set "DEFAULT_SESSION_ONLY = True" in the config area
near the top of __init__.py the "expires" attribute won't be set on
the session cookies and the cookies will not be persisted by browsers
(close the browser and the session is lost). There are times where
due to privacy policy or whatever that you may want to use non-
persistent sessions. The "lifetime" value (default to 7 days) is
still honored as normal so if a user keeps his browser open for 7 days
the session should still expire.

I made a couple other handy updates as well like specifying an
"APP_COOKIE_KEY" variable in the __init__.py config area (see the
"appengine_config.py in the zip file for how to import and use it).
It's also used in the DjangoSessionMiddleware class.

The other minor tweak was to add a "DEFAULT_SSL_ONLY = False" variable
in the config area of __init__.py to make it easy to change the
default ssl_only setting

I also changed COOKIE_OVERHEAD to use len(COOKIE_FMT_SECURE...)
instead of len(COOKIE_FMT...) since the former is the longer string

I hope you find the updates useful.

Download zip from: http://www.solipsis.com/gaesessions_session_only.zip