#4 use referrer for default page after logi

[Max Cooper]

Currently, users can specify a "default page" in the config
file to send users to after an unsolicited login submittal. For
cases where there is a login form on every page, it may be
desireable to return the user to the page they submitted the
login form from. This information could be obtained from
the referrer header of the login submittal. Update the code
to use the referrer when no default-page is specified in the
config file.