Description:
------------
function highlight_string() removes backslashes

Reproduce code:
---------------
<?php
$text = '<?php
$blah = 1;
\\this is a comment line with two backslashes at the beginning and one at the end:\
$blah = 2;
?>';
highlight_string($text);
?>

Expected result:
----------------
Expected output in the browser:

<?php
$blah = 1;
\\this is a comment line with two backslashes at the beginning and one at the end:\
$blah = 2;
?>

Actual result:
--------------
Actual output in the browser:

<?php 
$blah = 1; 
this is a comment line with two backslashes at the beginning and one at the end: 
$blah = 2; 
?>