Allows the user to pass the REMOTE_ADDR via the params hash

$ENV{REMOTE_ADDR} is not set by all/most we servers. This patch allows
the user to set it by passing it in the params hash to process(), ie:

    my $params =$c->req->params;
    $params->{REMOTE_ADDR} = $c->req->address;
    $form->process( item => $contact, params => $params );

It will fallback to $ENV{REMOTE_ADDR} if it is not in params, and it will
a croak with an explanation if neither are available.
Merge pull request #1 from mvgrimes/remote-addr

Allows the user to pass the REMOTE_ADDR via the params hash