Description:
------------
Please add support for the CTR encryption mode (MCRYPT_MODE_CTR).

See also attached patch against PHP 5.5.x which adds the necessary code and also defines a deprecated function mcrypt_ctr() (for consistency with other modes).

Test script:
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<?php

$key      = "FooBar";
$secret   = "PHP Testfest 2008";
$cipher   = MCRYPT_RIJNDAEL_128;
$iv       = mcrypt_create_iv(mcrypt_get_iv_size($cipher, MCRYPT_MODE_CTR), MCRYPT_RAND);
$enc_data = mcrypt_ctr($cipher, $key, $secret, MCRYPT_ENCRYPT, $iv);
var_dump(bin2hex($enc_data));

?>

Expected result:
----------------
string(34) "5e42855e8236dacdb8fafbdaa12d176f13"

Actual result:
--------------
Bunch of errors due to lack of MCRYPT_MODE_CTR constant and undefined function mcrypt_ctr().