When using the hook system, multiple auth hooks are dispatched, and hence creates multiple auth headers

Steps to reproduce - Use the following sript

$hooks = new Requests_Hooks();

$hooks->register('fsockopen.before_send', function (&$data){
    var_dump( $data );
});

$headers = array('Accept' => 'application/json');
$options = array('auth' => array('user', 'pass'), 'hooks' => $hooks, 'transport' => 'Requests_Transport_fsockopen');
$request = Requests::get('https://api.github.com/gists', $headers, $options);
$request = Requests::get('https://api.github.com/gists', $headers, $options);

The result from the above script execution

string(221) "GET /gists HTTP/1.0
Host: api.github.com:443
User-Agent: php-requests/1.6.1
Accept-Encoding: deflate;q=1.0, compress;q=0.5, gzip;q=0.5
Accept: application/json
Authorization: Basic dXNlcjpwYXNz
Connection: Close

"
string(256) "GET /gists HTTP/1.0
Host: api.github.com:443
User-Agent: php-requests/1.6.1
Accept-Encoding: deflate;q=1.0, compress;q=0.5, gzip;q=0.5
Accept: application/json
Authorization: Basic dXNlcjpwYXNz
Authorization: Basic dXNlcjpwYXNz
Connection: Close

"

Note that on the second request, there are two Authorization header. Similarly, for the third request, there will be three Authorization headers added to the request.

Start by running the reproduction script with Requests_Hooks, Requests::get, and the fsockopen.before_send hook, then trace how authentication headers are added across successive requests. Done means repeated requests using the same options produce only one Authorization header each.