The re-tweet intent itself has problems right now. It's been filed as a bug since November so I don't think you'll want to use the re-tweet functionality from an external website. You can simulate a re-tweet with a regular tweet intent and pre-filling in the text, (which sounds like what you actually want to do). With the tweet intent you send a HTTP request to https://twitter.com/intent/tweet
. You could then include the text
parameter to pre-fill the text when the HTTP request is sent, or the link is clicked.
Using your example it would look something like this:
<!-- HEADER -->
<?php
$randomThings = file('**responses.txt**', FILE_IGNORE_NEW_LINES | FILE_SKIP_EMPTY_LINES);
?>
<!-- CALL SCRIPT -->
<?php
$newThings = $randomThings[mt_rand(0,count($randomThings)-1)]; //must evaluate to a string
echo $newThings;
echo '<a href="https://twitter.com/intent/tweet?text='.$newThings.'">Link text</a>';
?>
this would be an unstyled link instead of a "button" but you can adapt it to be a button using standard HTML/CSS styling.
ref: https://dev.twitter.com/docs/intents