Revert "decode_value: check validity of refno"

The test looked at limits for the wrong program (the refno relates
to the program at depth depth).

Revert it for now as it breaks working code.

This reverts commit c88883e028a5182d0e0e8c668f2d672a9cc7e367.
Make sure we compile when HAVE_JPEGLIB_H is undefined.
Crypto.CCM: Added Counter with CBC-MAC mode.

This cipher mode is specified in NIST Special Publication 800-38C.
Crypto.GCM: Added some missing functions.

Adds digest_size().
Updated for Nettle API change.