[WIP] DTLS 1.0 preliminary patches

[Jonathan Bastien-Filiatrault]

Simon Josefsson wrote:
> Jonathan, how much code do you think DTLS will add?  Perhaps we should
> create a header file gnutls/dtls.h for the DTLS-specific APIs and create
> a separate library libgnutls-dtls for the DTLS-specific parts.
> 
> /Simon

Maybe... The bigger part of the code will be handshake retransmission 
and reassembly. Retransmission will probably use a linked list of 
packets and I am thinking of using a binary heap for reassembly. I don't 
think it will be huge. I am hoping that is the only logic I have to 
build from scratch (so far so good). At the very least I will have a 
gnutls_dtls_buffers.{c,h}.

Jonathan