3DES: Fixed ContinuousBuffer() in CTR/CFB/OFB

FIXED: multiple calls to enable/enableContinuousBuffer() work's now in CTR/CFB/OFB
FIXED: "Illegal string offset" and strlen(array()) Warning/Notice
Performance improvement in CFB Mode with enableContinuousBuffer() using MODE_MCRYPT
AES, DES, RC4, Rijndael, TripleDES: multiple changes

- apply petrich's TripleDES / CFB decrypt to AES and DES
- make DES use the updated _generate_xor
- correct a comment typo