#182 Portal: Enable cancel of search

[Adam Franco]

Allow users to cancel a search.

When doing so, be sure that the equivalent of the browser's 'stop' button
is done so that a RST TCP packet will be sent to the server. This will
allow PHP's connection_status()/connection_aborted() functions to work
and/or the PHP script will automatically terminate. The important thing is
if a user cancels the search, the server should stop working to process
it.

As well, incomplete search results shouldn't be added to the session. (just
check on this).