LP#1616501: teach mod_perl handlers how to detect client disconnects

LP#1616501: teach mod_perl handlers how to detect client disconnects

This patch provides an API so that mod_perl handlers
that act as OpenSRF clients have a way to specify that
if the browser disconnects, to stop trying to receive
results from an XMPP request.

To invoke it, mod_perl handlers can add the following:

use OpenSRF;
...
sub hander {
...
    my $r = shift;
    OpenSRF->OSRF_APACHE_REQUEST_OBJ($r);
...

Signed-off-by: Mike Rylander <mrylander@gmail.com>
Signed-off-by: Galen Charlton <gmc@equinoxinitiative.org>