Implemented current/reset/rewind/valid; Deleted test/mongocursor-constru...

...ctor.php and moved all cursor tests to mongoCursorTest.php. Passed basic student name query.

Test case is modeled after the first note/comment in http://php.net/manual/en/class.iterator.php#iterator.examples, with roughly the following format:

<?php
$it->rewind();
while ($it->valid())
{
    $key = $it->key();
    $value = $it->current();
    $it->next();
}
?>