In tiger, we currently look to see if we have the maximum space available
in the destination buffers before trying to encrypt/decrypt. We could be
a lot smarter about this, but don't have time at the moment. Address for
dragon, as this requires 14K chunks of memory to be free, even for just a
few bytes of payload.

For wrap, look at the buffer size, subtract off the max padding and
MAC sizes, then allow the result to be obtained from the src buffer.

For unwrap, look at the inbound buffers, subtract the max padding and MAC
sizes, then determine if there's enough to store.
 
###@###.### 2004-04-09