check 404 when downloading

This should prevent multiple http requests to the same url
update getURIInfo() to allow returning content

also, convert getURLInfo() to getURIInfo, to be constant with other method names.
Don't use the old filter class for 404s
update method name
be more consistent with terms
Don't cache requests where the content was requested

in theory, we could run out of memory if we store large amounts of content.  So, return before the details
are stored if we are supposed to return content.