fixed corrupted decrypt() in CTR mode

$buffer['encrypted'] (which is always empty) should be $buffer['ciphertext'] or buffered stream will get corrupt...

Example:
define('CRYPT_AES_MODE',CRYPT_AES_MODE_INTERNAL);//in MODE_MCRYPT all is fine
$aes = new Crypt_AES(CRYPT_AES_MODE_CTR);
$aes->setKey(':-8');
$aes->enableContinuousBuffer();
$plaintext = ':-):-):-):-):-):-)';
for($i=0; $i<strlen($plaintext); $i++) {
 echo $aes->Decrypt($aes->Encrypt($plaintext[$i]));
}

Output:
:-):-):-):-):-):-(

Expected:
:-):-):-):-):-):-)


After Bugfix, output is:
:-):-):-):-):-):-)
Merge pull request #43 from petrich/patch-1

fixed corrupted decrypt() in CTR mode
[issue/39] Abstract test case for Crypt_AES.
[issue/39] Test case for Github ContinuousBuffer issue 39.
[issue/39] Extend tests to cover other modes. Also IVs, keys, etc.