Description:
------------
When using pcntl_fork() with the new MongoDB\Driver it is impossible to create a new MongoDB manager in the child process if one has been opened in the parent process.

Test script:
---------------
$manager1 = MongoDB\Driver\Manager('mongodb://localhost:27017');

$pid = pcntl_fork();

if ($pid == 0)
{
   // Child process, create a new manager here
   unset($manager1);
   $manager2 = MongoDB\Driver\Manager('mongodb://localhost:27017');

   // Perform queries with $manager2 here
}
else
{
   // Parent process, retain old manager
   // Perform queries with $manager1 here
}

Expected result:
----------------
Expected to have a new MongoDB connection in $manager2 that the child process can use.

Actual result:
--------------
Both managers, even the newly created on in the child process seem to share a socket to MongoDB and throw errors based on receiving each others responses.